From c94915b3607fdaedc4c0fc0f7bc8b59d4eaa44ad Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 27 Feb 2026 11:28:42 +0530
Subject: [PATCH 01/14] Add multi-platform Docker image support (amd64 + arm64)

Enable native arm64 support for Apple Silicon users by building
multi-architecture images via buildx. Uses TARGETARCH for explicit
Go cross-compilation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 .github/workflows/go.yaml | 1 +
 Dockerfile                | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/go.yaml b/.github/workflows/go.yaml
index ac7802c..850e208 100644
--- a/.github/workflows/go.yaml
+++ b/.github/workflows/go.yaml
@@ -84,6 +84,7 @@ jobs:
           push: true
           context: .
           file: Dockerfile
+          platforms: linux/amd64,linux/arm64
           provenance: true
           sbom: true
           cache-from: type=gha
diff --git a/Dockerfile b/Dockerfile
index af9b5cd..6b08421 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -9,7 +9,9 @@ RUN go mod download
 
 # Copy source code (this layer changes frequently)
 COPY . .
-RUN CGO_ENABLED=0 go build -ldflags="-s -w" -o /app/main main.go
+
+ARG TARGETARCH
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=${TARGETARCH} go build -ldflags="-s -w" -o /app/main main.go
 
 # Final stage - distroless
 FROM gcr.io/distroless/static-debian12

From 24120979ec836aeae61d9533db2e982020c91286 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 27 Feb 2026 11:29:13 +0530
Subject: [PATCH 02/14] Update README.md with tag v0.0.7

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index c418cc2..fe46474 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,7 @@ To deploy the server, you need to build a Docker image using the provided `Docke
 ```dockerfile
 # Use the official static-server image as the base image
 # This will pull the prebuilt version of the static-server to run your static website
-FROM zopdev/static-server:v0.0.6
+FROM zopdev/static-server:v0.0.7
 
 # Copy static files into the container
 # The 'COPY' directive moves your static files (in this case, located at '/app/out') into the '/website' directory

From aa0c39232c03491e1041396f02d6f9a76b84b523 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 27 Feb 2026 11:37:58 +0530
Subject: [PATCH 03/14] Add QEMU setup for multi-platform Docker builds

Required for arm64 emulation on amd64 runners.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 .github/workflows/go.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.github/workflows/go.yaml b/.github/workflows/go.yaml
index 850e208..3d4896c 100644
--- a/.github/workflows/go.yaml
+++ b/.github/workflows/go.yaml
@@ -69,6 +69,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - uses: docker/setup-qemu-action@v3
+
       - uses: docker/setup-buildx-action@v3
 
       - uses: docker/login-action@v3

From ecb09f791cace98229aeb06e2bfa9f99a729cc58 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 27 Feb 2026 11:50:44 +0530
Subject: [PATCH 04/14] Use cross-compilation for multi-platform Docker builds

Replace QEMU emulation with native cross-compilation by adding
--platform=$BUILDPLATFORM to the build stage. Go cross-compiles
to the target architecture natively, eliminating slow emulation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 .github/workflows/go.yaml | 2 --
 Dockerfile                | 4 ++--
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/go.yaml b/.github/workflows/go.yaml
index 3d4896c..850e208 100644
--- a/.github/workflows/go.yaml
+++ b/.github/workflows/go.yaml
@@ -69,8 +69,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: docker/setup-qemu-action@v3
-
       - uses: docker/setup-buildx-action@v3
 
       - uses: docker/login-action@v3
diff --git a/Dockerfile b/Dockerfile
index 6b08421..8f1ed72 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
-# Build stage
-FROM golang:1.26 AS build
+# Build stage - runs on native platform, cross-compiles to target
+FROM --platform=$BUILDPLATFORM golang:1.26 AS build
 
 WORKDIR /src
 

From 3449b51b4db54fa74414ba6541a8cb2414556758 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 27 Feb 2026 12:04:59 +0530
Subject: [PATCH 05/14] Update GitHub Actions to latest versions and add image
 output
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- actions/checkout v4 → v6
- actions/setup-go v4 → v6 (caching now enabled by default)
- golangci/golangci-lint-action v8 → v9
- Add step to output pushed image registry path

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 .github/workflows/go.yaml | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/.github/workflows/go.yaml b/.github/workflows/go.yaml
index 850e208..6316773 100644
--- a/.github/workflows/go.yaml
+++ b/.github/workflows/go.yaml
@@ -12,11 +12,10 @@ jobs:
     runs-on: ubuntu-latest
     name: Test and Build
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-go@v4
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
         with:
           go-version: '1.26'
-          cache: true
       - name: Test
         run: go test ./...
 
@@ -24,12 +23,11 @@ jobs:
     name: Code Quality🎖️
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-go@v4
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
         with:
           go-version: '1.26'
-          cache: true
-      - uses: golangci/golangci-lint-action@v8
+      - uses: golangci/golangci-lint-action@v9
         with:
           version: v2.10.1
           args: --timeout 9m0s
@@ -67,7 +65,7 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: docker/setup-buildx-action@v3
 
@@ -91,3 +89,6 @@ jobs:
           cache-to: type=gha,mode=max
           tags: |
             ${{ vars.DOCKER_REGISTRY_TARGET }}:${{ env.RELEASE_VERSION }}
+
+      - name: Output Image Path
+        run: echo "Image pushed to ${{ vars.DOCKER_REGISTRY_TARGET }}:${{ env.RELEASE_VERSION }}"

From 519197faf980d57ccb296e26d5ec3b7dd17d61d7 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Thu, 5 Mar 2026 17:37:57 +0530
Subject: [PATCH 06/14] Added support for env hydration

---
 README.md    | 35 +++++++++++++++++++++-
 main.go      | 40 +++++++++++++++++++++++++
 main_test.go | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 158 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index fe46474..9f0e608 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,36 @@ A simple and efficient solution for serving static files.
   - The server serves files from the `static` directory by default, but you can change this by setting the `STATIC_DIR_PATH` environment variable.
   - Support all the confgs of the gofr framework - https://gofr.dev
 
+## Config File Hydration
+
+When the `CONFIG_FILE_PATH` environment variable is set, the server replaces any `${VAR}` placeholders in that file at startup using values from the environment (including `.env` files). The file is rewritten in-place before serving begins.
+
+This is useful for injecting runtime configuration into static front-end apps without rebuilding them.
+
+If any placeholders have no matching environment variable, the server still writes the file (substituting empty strings for missing values) and logs an error listing the unresolved variables.
+
+#### Example
+
+Given a `config.json` template:
+
+```json
+{
+  "clientId": "${GOOGLE_CLIENT_ID}",
+  "apiUrl": "${API_BASE_URL}"
+}
+```
+
+If `GOOGLE_CLIENT_ID=abc123` and `API_BASE_URL=https://api.example.com` are set, the file becomes:
+
+```json
+{
+  "clientId": "abc123",
+  "apiUrl": "https://api.example.com"
+}
+```
+
+> See the [example Dockerfile](#1-build-a-docker-image) below for how to set `CONFIG_FILE_PATH`.
+
 ## Usage
 
 ### 1. Build a Docker image
@@ -22,13 +52,16 @@ To deploy the server, you need to build a Docker image using the provided `Docke
 ```dockerfile
 # Use the official static-server image as the base image
 # This will pull the prebuilt version of the static-server to run your static website
-FROM zopdev/static-server:v0.0.7
+FROM zopdev/static-server:v0.0.8
 
 # Copy static files into the container
 # The 'COPY' directive moves your static files (in this case, located at '/app/out') into the '/website' directory
 # which is where the static server expects to find the files to serve
 COPY /app/out /static
 
+# Set the path to the config file for environment variable hydration at startup
+ENV CONFIG_FILE_PATH=/static/config.json
+
 # Expose the port on which the server will run
 # By default, the server listens on port 8000, so we expose that port to allow access from outside the container
 EXPOSE 8000
diff --git a/main.go b/main.go
index f510abe..fb7778b 100644
--- a/main.go
+++ b/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -8,6 +9,7 @@ import (
 	"strings"
 
 	"gofr.dev/pkg/gofr"
+	"gofr.dev/pkg/gofr/config"
 )
 
 const defaultStaticFilePath = `./static`
@@ -15,9 +17,47 @@ const indexHTML = "/index.html"
 const htmlExtension = ".html"
 const rootPath = "/"
 
+func hydrateConfig(cfg config.Config) error {
+	configPath := cfg.Get("CONFIG_FILE_PATH")
+	if configPath == "" {
+		return nil
+	}
+
+	content, err := os.ReadFile(configPath)
+	if err != nil {
+		return fmt.Errorf("failed to read config file: %w", err)
+	}
+
+	// Hydrate with available vars
+	result := os.Expand(string(content), cfg.Get)
+
+	if err := os.WriteFile(configPath, []byte(result), 0644); err != nil {
+		return fmt.Errorf("failed to write config file: %w", err)
+	}
+
+	// Detect vars that were missing (replaced with empty string)
+	re := regexp.MustCompile(`\$\{(\w+)\}`)
+	matches := re.FindAllStringSubmatch(string(content), -1)
+	var missing []string
+	for _, m := range matches {
+		if cfg.Get(m[1]) == "" {
+			missing = append(missing, m[1])
+		}
+	}
+	if len(missing) > 0 {
+		return fmt.Errorf("missing config variables: %v", missing)
+	}
+
+	return nil
+}
+
 func main() {
 	app := gofr.New()
 
+	if err := hydrateConfig(app.Config); err != nil {
+		app.Logger().Error(err)
+	}
+
 	staticFilePath := app.Config.GetOrDefault("STATIC_DIR_PATH", defaultStaticFilePath)
 
 	app.UseMiddleware(func(h http.Handler) http.Handler {
diff --git a/main_test.go b/main_test.go
index a85a037..82afacb 100644
--- a/main_test.go
+++ b/main_test.go
@@ -7,8 +7,92 @@ import (
 	"path/filepath"
 	"testing"
 	"time"
+
+	"gofr.dev/pkg/gofr/config"
 )
 
+func TestHydrateConfig(t *testing.T) {
+	tests := []struct {
+		name     string
+		template string
+		vars     map[string]string
+		expected string
+		wantErr  bool
+	}{
+		{
+			name:     "hydrates config in-place",
+			template: `{"a":"${A}","b":"${B}"}`,
+			vars:     map[string]string{"A": "1", "B": "2"},
+			expected: `{"a":"1","b":"2"}`,
+			wantErr:  false,
+		},
+		{
+			name:    "no-op when config path empty",
+			vars:    map[string]string{},
+			wantErr: false,
+		},
+		{
+			name:     "extra config vars not in template",
+			template: `{"a":"${A}"}`,
+			vars:     map[string]string{"A": "1", "EXTRA": "x"},
+			expected: `{"a":"1"}`,
+			wantErr:  false,
+		},
+		{
+			name:     "some template vars missing",
+			template: `{"a":"${A}","b":"${MISSING}"}`,
+			vars:     map[string]string{"A": "1"},
+			expected: `{"a":"1","b":""}`,
+			wantErr:  true,
+		},
+		{
+			name:     "all template vars missing",
+			template: `{"a":"${X}","b":"${Y}"}`,
+			vars:     map[string]string{},
+			expected: `{"a":"","b":""}`,
+			wantErr:  true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			vars := make(map[string]string)
+			for k, v := range tt.vars {
+				vars[k] = v
+			}
+
+			if tt.template != "" {
+				dir := t.TempDir()
+				configFile := filepath.Join(dir, "config.json")
+				if err := os.WriteFile(configFile, []byte(tt.template), 0644); err != nil {
+					t.Fatalf("failed to write config: %v", err)
+				}
+				vars["CONFIG_FILE_PATH"] = configFile
+			}
+
+			cfg := config.NewMockConfig(vars)
+			err := hydrateConfig(cfg)
+
+			if tt.wantErr && err == nil {
+				t.Fatal("expected error, got nil")
+			}
+			if !tt.wantErr && err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			if tt.template != "" {
+				output, err := os.ReadFile(vars["CONFIG_FILE_PATH"])
+				if err != nil {
+					t.Fatalf("failed to read config: %v", err)
+				}
+				if string(output) != tt.expected {
+					t.Errorf("expected %q, got %q", tt.expected, string(output))
+				}
+			}
+		})
+	}
+}
+
 func TestServer(t *testing.T) {
 	// Create a temporary directory
 	//nolint:staticcheck // Ignore as we are testing the server

From 18fa6b99df84d5984c8e6a6ad157f547c7db100a Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Thu, 5 Mar 2026 17:42:25 +0530
Subject: [PATCH 07/14] Updated README.md

---
 README.md | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/README.md b/README.md
index 9f0e608..095d8d9 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ A simple and efficient solution for serving static files.
 - **Lightweight**: Minimal dependencies for optimal performance.
 - **Configurable**: You can easily configure the server or extend it based on your needs.
   - The server serves files from the `static` directory by default, but you can change this by setting the `STATIC_DIR_PATH` environment variable.
-  - Support all the confgs of the gofr framework - https://gofr.dev
+  - Support all the configs of the gofr framework - https://gofr.dev
 
 ## Config File Hydration
 
@@ -55,20 +55,17 @@ To deploy the server, you need to build a Docker image using the provided `Docke
 FROM zopdev/static-server:v0.0.8
 
 # Copy static files into the container
-# The 'COPY' directive moves your static files (in this case, located at '/app/out') into the '/website' directory
+# The 'COPY' directive moves your static files (in this case, located at '/app/out') into the '/static' directory
 # which is where the static server expects to find the files to serve
 COPY /app/out /static
 
 # Set the path to the config file for environment variable hydration at startup
 ENV CONFIG_FILE_PATH=/static/config.json
 
-# Expose the port on which the server will run
-# By default, the server listens on port 8000, so we expose that port to allow access from outside the container
-EXPOSE 8000
+# The server listens on port 8000 by default; set HTTP_PORT to change it
 
 # Define the command to run the server
-# The static server is started with the '/main' binary included in the image, which will start serving
-# the files from the '/website' directory on port 8000
+# The static server is started with the '/main' binary included in the image
 CMD ["/main"]
 ```
 
@@ -108,7 +105,7 @@ Your static files will be served, and the root (`/`) will typically display your
 
 ## Notes
 
-- The server serves all files in the `website` directory, so make sure to avoid any sensitive files or configuration details in that directory.
+- The server serves all files in the `static` directory, so make sure to avoid any sensitive files or configuration details in that directory.
 
 ## License
 

From 5c8a53f3909196316bbcba431c9c4d9e0515bae2 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 6 Mar 2026 14:51:12 +0530
Subject: [PATCH 08/14] Code refactor

---
 go.mod                          |   8 +-
 internal/config/hydrate.go      |  65 +++++++++++++++
 internal/config/hydrate_test.go | 137 ++++++++++++++++++++++++++++++++
 main.go                         |  48 +++--------
 main_test.go                    |  84 --------------------
 5 files changed, 216 insertions(+), 126 deletions(-)
 create mode 100644 internal/config/hydrate.go
 create mode 100644 internal/config/hydrate_test.go

diff --git a/go.mod b/go.mod
index d165ee2..b9457b2 100644
--- a/go.mod
+++ b/go.mod
@@ -2,7 +2,11 @@ module zop.dev/static-server
 
 go 1.25.0
 
-require gofr.dev v1.54.3
+require (
+	github.com/stretchr/testify v1.11.1
+	go.uber.org/mock v0.6.0
+	gofr.dev v1.54.3
+)
 
 require (
 	cloud.google.com/go v0.123.0 // indirect
@@ -57,7 +61,6 @@ require (
 	github.com/redis/go-redis/v9 v9.17.3 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/segmentio/kafka-go v0.4.50 // indirect
-	github.com/stretchr/testify v1.11.1 // indirect
 	github.com/xdg-go/pbkdf2 v1.0.0 // indirect
 	github.com/xdg-go/scram v1.2.0 // indirect
 	github.com/xdg-go/stringprep v1.0.4 // indirect
@@ -76,7 +79,6 @@ require (
 	go.opentelemetry.io/otel/sdk/metric v1.40.0 // indirect
 	go.opentelemetry.io/otel/trace v1.40.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.9.0 // indirect
-	go.uber.org/mock v0.6.0 // indirect
 	go.yaml.in/yaml/v2 v2.4.3 // indirect
 	golang.org/x/crypto v0.48.0 // indirect
 	golang.org/x/exp v0.0.0-20260218203240-3dfff04db8fa // indirect
diff --git a/internal/config/hydrate.go b/internal/config/hydrate.go
new file mode 100644
index 0000000..c41b523
--- /dev/null
+++ b/internal/config/hydrate.go
@@ -0,0 +1,65 @@
+package config
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"regexp"
+
+	"gofr.dev/pkg/gofr/config"
+	"gofr.dev/pkg/gofr/datasource/file"
+)
+
+var (
+	ErrMissingVars = errors.New("missing config variables")
+	ErrReadConfig  = errors.New("failed to read config file")
+	ErrWriteConfig = errors.New("failed to write config file")
+	ErrMissingFile = errors.New("file not found")
+
+	envVarRe = regexp.MustCompile(`\$\{(\w+)\}`)
+)
+
+const filePathVar = "CONFIG_FILE_PATH"
+
+func HydrateFile(fs file.FileSystem, cfg config.Config) error {
+	configPath := cfg.Get(filePathVar)
+	if configPath == "" {
+		return nil
+	}
+
+	configFile, err := fs.Open(filepath.Clean(configPath))
+	if err != nil {
+		return fmt.Errorf("%w: %w", ErrReadConfig, err)
+	}
+
+	content, err := io.ReadAll(configFile)
+	if err != nil {
+		return fmt.Errorf("%w: %w", ErrReadConfig, err)
+	}
+
+	// Hydrate with available vars
+	result := os.Expand(string(content), cfg.Get)
+
+	if _, err = configFile.Write([]byte(result)); err != nil {
+		return fmt.Errorf("%w: %w", ErrWriteConfig, err)
+	}
+
+	// Detect vars that were missing (replaced with empty string)
+	matches := envVarRe.FindAllStringSubmatch(string(content), -1)
+
+	var missing []string
+
+	for _, m := range matches {
+		if cfg.Get(m[1]) == "" {
+			missing = append(missing, m[1])
+		}
+	}
+
+	if len(missing) > 0 {
+		return fmt.Errorf("%w: %v", ErrMissingVars, missing)
+	}
+
+	return nil
+}
diff --git a/internal/config/hydrate_test.go b/internal/config/hydrate_test.go
new file mode 100644
index 0000000..1d8945b
--- /dev/null
+++ b/internal/config/hydrate_test.go
@@ -0,0 +1,137 @@
+package config
+
+import (
+	"errors"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.uber.org/mock/gomock"
+	"gofr.dev/pkg/gofr/config"
+	"gofr.dev/pkg/gofr/datasource/file"
+)
+
+var (
+	errDiskFailure = errors.New("disk failure")
+	errDiskFull    = errors.New("disk full")
+)
+
+func TestConfig(t *testing.T) {
+	tests := []struct {
+		name     string
+		template string
+		vars     map[string]string
+		expected string
+		wantErr  error
+	}{
+		{
+			name:     "all vars present",
+			template: `{"a":"${A}","b":"${B}"}`,
+			vars:     map[string]string{"A": "1", "B": "2"},
+			expected: `{"a":"1","b":"2"}`,
+		},
+		{
+			name:    "no config path is a no-op",
+			vars:    map[string]string{},
+			wantErr: nil,
+		},
+		{
+			name:     "extra vars ignored",
+			template: `{"a":"${A}"}`,
+			vars:     map[string]string{"A": "1", "EXTRA": "x"},
+			expected: `{"a":"1"}`,
+		},
+		{
+			name:     "partial vars missing",
+			template: `{"a":"${A}","b":"${MISSING}"}`,
+			vars:     map[string]string{"A": "1"},
+			expected: `{"a":"1","b":""}`,
+			wantErr:  ErrMissingVars,
+		},
+		{
+			name:     "all vars missing",
+			template: `{"a":"${X}","b":"${Y}"}`,
+			vars:     map[string]string{},
+			expected: `{"a":"","b":""}`,
+			wantErr:  ErrMissingVars,
+		},
+		{
+			name:    "invalid config path",
+			vars:    map[string]string{"CONFIG_FILE_PATH": "/no/such/file"},
+			wantErr: ErrReadConfig,
+		},
+		{
+			name:     "read error",
+			template: "read-error",
+			vars:     map[string]string{},
+			wantErr:  ErrReadConfig,
+		},
+		{
+			name:     "write error",
+			template: "write-error",
+			vars:     map[string]string{},
+			wantErr:  ErrWriteConfig,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			mockFS := file.NewMockFileSystem(ctrl)
+
+			gotOutput := setupMocks(t, ctrl, mockFS, tt.template, tt.vars)
+
+			err := HydrateFile(mockFS, config.NewMockConfig(tt.vars))
+
+			require.ErrorIs(t, err, tt.wantErr)
+			require.Equal(t, tt.expected, string(gotOutput()))
+		})
+	}
+}
+
+func setupMocks(
+	t *testing.T, ctrl *gomock.Controller, mockFS *file.MockFileSystem,
+	template string, vars map[string]string,
+) func() []byte {
+	t.Helper()
+
+	var output []byte
+
+	switch {
+	case template != "":
+		vars[filePathVar] = "/mock/config.json"
+		mockFile := file.NewMockFile(ctrl)
+		mockFS.EXPECT().Open(vars[filePathVar]).Return(mockFile, nil)
+
+		setupReadWrite(mockFile, template, &output)
+
+	case vars[filePathVar] != "":
+		mockFS.EXPECT().Open(vars[filePathVar]).Return(nil, ErrMissingFile)
+	}
+
+	return func() []byte { return output }
+}
+
+func setupReadWrite(mockFile *file.MockFile, template string, output *[]byte) {
+	if template == "read-error" {
+		mockFile.EXPECT().Read(gomock.Any()).Return(0, errDiskFailure)
+		return
+	}
+
+	templateBytes := []byte(template)
+
+	mockFile.EXPECT().Read(gomock.Any()).DoAndReturn(func(p []byte) (int, error) {
+		n := copy(p, templateBytes)
+		return n, io.EOF
+	})
+
+	if template == "write-error" {
+		mockFile.EXPECT().Write(gomock.Any()).Return(0, errDiskFull)
+		return
+	}
+
+	mockFile.EXPECT().Write(gomock.Any()).DoAndReturn(func(p []byte) (int, error) {
+		*output = append([]byte{}, p...)
+		return len(p), nil
+	})
+}
diff --git a/main.go b/main.go
index fb7778b..249a62c 100644
--- a/main.go
+++ b/main.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"fmt"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -9,7 +8,8 @@ import (
 	"strings"
 
 	"gofr.dev/pkg/gofr"
-	"gofr.dev/pkg/gofr/config"
+
+	"zop.dev/static-server/internal/config"
 )
 
 const defaultStaticFilePath = `./static`
@@ -17,46 +17,16 @@ const indexHTML = "/index.html"
 const htmlExtension = ".html"
 const rootPath = "/"
 
-func hydrateConfig(cfg config.Config) error {
-	configPath := cfg.Get("CONFIG_FILE_PATH")
-	if configPath == "" {
-		return nil
-	}
-
-	content, err := os.ReadFile(configPath)
-	if err != nil {
-		return fmt.Errorf("failed to read config file: %w", err)
-	}
-
-	// Hydrate with available vars
-	result := os.Expand(string(content), cfg.Get)
-
-	if err := os.WriteFile(configPath, []byte(result), 0644); err != nil {
-		return fmt.Errorf("failed to write config file: %w", err)
-	}
-
-	// Detect vars that were missing (replaced with empty string)
-	re := regexp.MustCompile(`\$\{(\w+)\}`)
-	matches := re.FindAllStringSubmatch(string(content), -1)
-	var missing []string
-	for _, m := range matches {
-		if cfg.Get(m[1]) == "" {
-			missing = append(missing, m[1])
-		}
-	}
-	if len(missing) > 0 {
-		return fmt.Errorf("missing config variables: %v", missing)
-	}
-
-	return nil
-}
-
 func main() {
 	app := gofr.New()
 
-	if err := hydrateConfig(app.Config); err != nil {
-		app.Logger().Error(err)
-	}
+	app.OnStart(func(ctx *gofr.Context) error {
+		if err := config.HydrateFile(ctx.File, app.Config); err != nil {
+			ctx.Logger.Error(err)
+		}
+
+		return nil
+	})
 
 	staticFilePath := app.Config.GetOrDefault("STATIC_DIR_PATH", defaultStaticFilePath)
 
diff --git a/main_test.go b/main_test.go
index 82afacb..a85a037 100644
--- a/main_test.go
+++ b/main_test.go
@@ -7,92 +7,8 @@ import (
 	"path/filepath"
 	"testing"
 	"time"
-
-	"gofr.dev/pkg/gofr/config"
 )
 
-func TestHydrateConfig(t *testing.T) {
-	tests := []struct {
-		name     string
-		template string
-		vars     map[string]string
-		expected string
-		wantErr  bool
-	}{
-		{
-			name:     "hydrates config in-place",
-			template: `{"a":"${A}","b":"${B}"}`,
-			vars:     map[string]string{"A": "1", "B": "2"},
-			expected: `{"a":"1","b":"2"}`,
-			wantErr:  false,
-		},
-		{
-			name:    "no-op when config path empty",
-			vars:    map[string]string{},
-			wantErr: false,
-		},
-		{
-			name:     "extra config vars not in template",
-			template: `{"a":"${A}"}`,
-			vars:     map[string]string{"A": "1", "EXTRA": "x"},
-			expected: `{"a":"1"}`,
-			wantErr:  false,
-		},
-		{
-			name:     "some template vars missing",
-			template: `{"a":"${A}","b":"${MISSING}"}`,
-			vars:     map[string]string{"A": "1"},
-			expected: `{"a":"1","b":""}`,
-			wantErr:  true,
-		},
-		{
-			name:     "all template vars missing",
-			template: `{"a":"${X}","b":"${Y}"}`,
-			vars:     map[string]string{},
-			expected: `{"a":"","b":""}`,
-			wantErr:  true,
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			vars := make(map[string]string)
-			for k, v := range tt.vars {
-				vars[k] = v
-			}
-
-			if tt.template != "" {
-				dir := t.TempDir()
-				configFile := filepath.Join(dir, "config.json")
-				if err := os.WriteFile(configFile, []byte(tt.template), 0644); err != nil {
-					t.Fatalf("failed to write config: %v", err)
-				}
-				vars["CONFIG_FILE_PATH"] = configFile
-			}
-
-			cfg := config.NewMockConfig(vars)
-			err := hydrateConfig(cfg)
-
-			if tt.wantErr && err == nil {
-				t.Fatal("expected error, got nil")
-			}
-			if !tt.wantErr && err != nil {
-				t.Fatalf("unexpected error: %v", err)
-			}
-
-			if tt.template != "" {
-				output, err := os.ReadFile(vars["CONFIG_FILE_PATH"])
-				if err != nil {
-					t.Fatalf("failed to read config: %v", err)
-				}
-				if string(output) != tt.expected {
-					t.Errorf("expected %q, got %q", tt.expected, string(output))
-				}
-			}
-		})
-	}
-}
-
 func TestServer(t *testing.T) {
 	// Create a temporary directory
 	//nolint:staticcheck // Ignore as we are testing the server

From fb75fc45f79df9932c2a4e4621eb77a48932576b Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 6 Mar 2026 16:20:28 +0530
Subject: [PATCH 09/14] Fixed implementation

---
 internal/config/hydrate.go      |   9 ++-
 internal/config/hydrate_test.go | 102 ++++++++++++--------------------
 2 files changed, 47 insertions(+), 64 deletions(-)

diff --git a/internal/config/hydrate.go b/internal/config/hydrate.go
index c41b523..fa826af 100644
--- a/internal/config/hydrate.go
+++ b/internal/config/hydrate.go
@@ -39,10 +39,17 @@ func HydrateFile(fs file.FileSystem, cfg config.Config) error {
 		return fmt.Errorf("%w: %w", ErrReadConfig, err)
 	}
 
+	configFile.Close()
+
 	// Hydrate with available vars
 	result := os.Expand(string(content), cfg.Get)
 
-	if _, err = configFile.Write([]byte(result)); err != nil {
+	wf, err := fs.OpenFile(configPath, os.O_WRONLY|os.O_TRUNC, 0)
+	if err != nil {
+		return fmt.Errorf("%w: %w", ErrWriteConfig, err)
+	}
+
+	if _, err = wf.Write([]byte(result)); err != nil {
 		return fmt.Errorf("%w: %w", ErrWriteConfig, err)
 	}
 
diff --git a/internal/config/hydrate_test.go b/internal/config/hydrate_test.go
index 1d8945b..784cd5d 100644
--- a/internal/config/hydrate_test.go
+++ b/internal/config/hydrate_test.go
@@ -1,20 +1,28 @@
 package config
 
 import (
-	"errors"
-	"io"
+	"os"
+	"path/filepath"
+	"runtime"
 	"testing"
 
 	"github.com/stretchr/testify/require"
-	"go.uber.org/mock/gomock"
 	"gofr.dev/pkg/gofr/config"
 	"gofr.dev/pkg/gofr/datasource/file"
+	"gofr.dev/pkg/gofr/logging"
 )
 
-var (
-	errDiskFailure = errors.New("disk failure")
-	errDiskFull    = errors.New("disk full")
-)
+func writeTempFile(t *testing.T, content string) string {
+	t.Helper()
+
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.json")
+
+	err := os.WriteFile(path, []byte(content), 0644)
+	require.NoError(t, err)
+
+	return path
+}
 
 func TestConfig(t *testing.T) {
 	tests := []struct {
@@ -60,78 +68,46 @@ func TestConfig(t *testing.T) {
 			vars:    map[string]string{"CONFIG_FILE_PATH": "/no/such/file"},
 			wantErr: ErrReadConfig,
 		},
-		{
-			name:     "read error",
-			template: "read-error",
-			vars:     map[string]string{},
-			wantErr:  ErrReadConfig,
-		},
-		{
-			name:     "write error",
-			template: "write-error",
-			vars:     map[string]string{},
-			wantErr:  ErrWriteConfig,
-		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			ctrl := gomock.NewController(t)
-			mockFS := file.NewMockFileSystem(ctrl)
+			fs := file.New(logging.NewMockLogger(logging.ERROR))
 
-			gotOutput := setupMocks(t, ctrl, mockFS, tt.template, tt.vars)
+			if tt.template != "" {
+				path := writeTempFile(t, tt.template)
+				tt.vars[filePathVar] = path
+			}
 
-			err := HydrateFile(mockFS, config.NewMockConfig(tt.vars))
+			err := HydrateFile(fs, config.NewMockConfig(tt.vars))
 
 			require.ErrorIs(t, err, tt.wantErr)
-			require.Equal(t, tt.expected, string(gotOutput()))
-		})
-	}
-}
-
-func setupMocks(
-	t *testing.T, ctrl *gomock.Controller, mockFS *file.MockFileSystem,
-	template string, vars map[string]string,
-) func() []byte {
-	t.Helper()
 
-	var output []byte
-
-	switch {
-	case template != "":
-		vars[filePathVar] = "/mock/config.json"
-		mockFile := file.NewMockFile(ctrl)
-		mockFS.EXPECT().Open(vars[filePathVar]).Return(mockFile, nil)
-
-		setupReadWrite(mockFile, template, &output)
-
-	case vars[filePathVar] != "":
-		mockFS.EXPECT().Open(vars[filePathVar]).Return(nil, ErrMissingFile)
+			if tt.expected != "" {
+				got, readErr := os.ReadFile(tt.vars[filePathVar])
+				require.NoError(t, readErr)
+				require.Equal(t, tt.expected, string(got))
+			}
+		})
 	}
-
-	return func() []byte { return output }
 }
 
-func setupReadWrite(mockFile *file.MockFile, template string, output *[]byte) {
-	if template == "read-error" {
-		mockFile.EXPECT().Read(gomock.Any()).Return(0, errDiskFailure)
-		return
+func TestHydrateFile_WriteError(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("chmod not effective on Windows")
 	}
 
-	templateBytes := []byte(template)
+	path := writeTempFile(t, `{"a":"${A}"}`)
 
-	mockFile.EXPECT().Read(gomock.Any()).DoAndReturn(func(p []byte) (int, error) {
-		n := copy(p, templateBytes)
-		return n, io.EOF
-	})
+	err := os.Chmod(path, 0444)
+	require.NoError(t, err)
 
-	if template == "write-error" {
-		mockFile.EXPECT().Write(gomock.Any()).Return(0, errDiskFull)
-		return
+	fs := file.New(logging.NewMockLogger(logging.ERROR))
+	vars := map[string]string{
+		filePathVar: path,
+		"A":         "1",
 	}
 
-	mockFile.EXPECT().Write(gomock.Any()).DoAndReturn(func(p []byte) (int, error) {
-		*output = append([]byte{}, p...)
-		return len(p), nil
-	})
+	err = HydrateFile(fs, config.NewMockConfig(vars))
+	require.ErrorIs(t, err, ErrWriteConfig)
 }

From d54c4e368c13c21e9a4b702805b060a56643d338 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 6 Mar 2026 16:34:46 +0530
Subject: [PATCH 10/14] Fixed linter issues

---
 internal/config/hydrate.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/internal/config/hydrate.go b/internal/config/hydrate.go
index fa826af..2af836b 100644
--- a/internal/config/hydrate.go
+++ b/internal/config/hydrate.go
@@ -39,7 +39,7 @@ func HydrateFile(fs file.FileSystem, cfg config.Config) error {
 		return fmt.Errorf("%w: %w", ErrReadConfig, err)
 	}
 
-	configFile.Close()
+	_ = configFile.Close()
 
 	// Hydrate with available vars
 	result := os.Expand(string(content), cfg.Get)

From 8f96c8e8c17c405e437f840666527117ca5c091b Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Fri, 6 Mar 2026 17:00:33 +0530
Subject: [PATCH 11/14] Converted fields to unexported

---
 internal/config/hydrate.go      | 17 ++++++++---------
 internal/config/hydrate_test.go |  8 ++++----
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/internal/config/hydrate.go b/internal/config/hydrate.go
index 2af836b..4f62518 100644
--- a/internal/config/hydrate.go
+++ b/internal/config/hydrate.go
@@ -13,10 +13,9 @@ import (
 )
 
 var (
-	ErrMissingVars = errors.New("missing config variables")
-	ErrReadConfig  = errors.New("failed to read config file")
-	ErrWriteConfig = errors.New("failed to write config file")
-	ErrMissingFile = errors.New("file not found")
+	errMissingVars = errors.New("missing config variables")
+	errReadConfig  = errors.New("failed to read config file")
+	errWriteConfig = errors.New("failed to write config file")
 
 	envVarRe = regexp.MustCompile(`\$\{(\w+)\}`)
 )
@@ -31,12 +30,12 @@ func HydrateFile(fs file.FileSystem, cfg config.Config) error {
 
 	configFile, err := fs.Open(filepath.Clean(configPath))
 	if err != nil {
-		return fmt.Errorf("%w: %w", ErrReadConfig, err)
+		return fmt.Errorf("%w: %w", errReadConfig, err)
 	}
 
 	content, err := io.ReadAll(configFile)
 	if err != nil {
-		return fmt.Errorf("%w: %w", ErrReadConfig, err)
+		return fmt.Errorf("%w: %w", errReadConfig, err)
 	}
 
 	_ = configFile.Close()
@@ -46,11 +45,11 @@ func HydrateFile(fs file.FileSystem, cfg config.Config) error {
 
 	wf, err := fs.OpenFile(configPath, os.O_WRONLY|os.O_TRUNC, 0)
 	if err != nil {
-		return fmt.Errorf("%w: %w", ErrWriteConfig, err)
+		return fmt.Errorf("%w: %w", errWriteConfig, err)
 	}
 
 	if _, err = wf.Write([]byte(result)); err != nil {
-		return fmt.Errorf("%w: %w", ErrWriteConfig, err)
+		return fmt.Errorf("%w: %w", errWriteConfig, err)
 	}
 
 	// Detect vars that were missing (replaced with empty string)
@@ -65,7 +64,7 @@ func HydrateFile(fs file.FileSystem, cfg config.Config) error {
 	}
 
 	if len(missing) > 0 {
-		return fmt.Errorf("%w: %v", ErrMissingVars, missing)
+		return fmt.Errorf("%w: %v", errMissingVars, missing)
 	}
 
 	return nil
diff --git a/internal/config/hydrate_test.go b/internal/config/hydrate_test.go
index 784cd5d..743ba07 100644
--- a/internal/config/hydrate_test.go
+++ b/internal/config/hydrate_test.go
@@ -54,19 +54,19 @@ func TestConfig(t *testing.T) {
 			template: `{"a":"${A}","b":"${MISSING}"}`,
 			vars:     map[string]string{"A": "1"},
 			expected: `{"a":"1","b":""}`,
-			wantErr:  ErrMissingVars,
+			wantErr:  errMissingVars,
 		},
 		{
 			name:     "all vars missing",
 			template: `{"a":"${X}","b":"${Y}"}`,
 			vars:     map[string]string{},
 			expected: `{"a":"","b":""}`,
-			wantErr:  ErrMissingVars,
+			wantErr:  errMissingVars,
 		},
 		{
 			name:    "invalid config path",
 			vars:    map[string]string{"CONFIG_FILE_PATH": "/no/such/file"},
-			wantErr: ErrReadConfig,
+			wantErr: errReadConfig,
 		},
 	}
 
@@ -109,5 +109,5 @@ func TestHydrateFile_WriteError(t *testing.T) {
 	}
 
 	err = HydrateFile(fs, config.NewMockConfig(vars))
-	require.ErrorIs(t, err, ErrWriteConfig)
+	require.ErrorIs(t, err, errWriteConfig)
 }

From 46b3f7a3343609b5859caac4b3629afa1017de9d Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Sat, 7 Mar 2026 14:25:06 +0530
Subject: [PATCH 12/14] Updated tests

---
 internal/config/hydrate_test.go | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/internal/config/hydrate_test.go b/internal/config/hydrate_test.go
index 743ba07..81fb99a 100644
--- a/internal/config/hydrate_test.go
+++ b/internal/config/hydrate_test.go
@@ -1,6 +1,7 @@
 package config
 
 import (
+	"io"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -12,15 +13,20 @@ import (
 	"gofr.dev/pkg/gofr/logging"
 )
 
-func writeTempFile(t *testing.T, content string) string {
+func writeTempFile(t *testing.T, fs file.FileSystem, content string) string {
 	t.Helper()
 
 	dir := t.TempDir()
 	path := filepath.Join(dir, "config.json")
 
-	err := os.WriteFile(path, []byte(content), 0644)
+	f, err := fs.Create(path)
 	require.NoError(t, err)
 
+	_, err = f.Write([]byte(content))
+	require.NoError(t, err)
+
+	require.NoError(t, f.Close())
+
 	return path
 }
 
@@ -75,7 +81,7 @@ func TestConfig(t *testing.T) {
 			fs := file.New(logging.NewMockLogger(logging.ERROR))
 
 			if tt.template != "" {
-				path := writeTempFile(t, tt.template)
+				path := writeTempFile(t, fs, tt.template)
 				tt.vars[filePathVar] = path
 			}
 
@@ -84,7 +90,9 @@ func TestConfig(t *testing.T) {
 			require.ErrorIs(t, err, tt.wantErr)
 
 			if tt.expected != "" {
-				got, readErr := os.ReadFile(tt.vars[filePathVar])
+				rf, readErr := fs.Open(tt.vars[filePathVar])
+				require.NoError(t, readErr)
+				got, readErr := io.ReadAll(rf)
 				require.NoError(t, readErr)
 				require.Equal(t, tt.expected, string(got))
 			}
@@ -97,12 +105,11 @@ func TestHydrateFile_WriteError(t *testing.T) {
 		t.Skip("chmod not effective on Windows")
 	}
 
-	path := writeTempFile(t, `{"a":"${A}"}`)
+	fs := file.New(logging.NewMockLogger(logging.ERROR))
+	path := writeTempFile(t, fs, `{"a":"${A}"}`)
 
 	err := os.Chmod(path, 0444)
 	require.NoError(t, err)
-
-	fs := file.New(logging.NewMockLogger(logging.ERROR))
 	vars := map[string]string{
 		filePathVar: path,
 		"A":         "1",

From ff25bad4c7c3d2950f24ad25687c0fb1c2ae63fb Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Sat, 7 Mar 2026 14:40:50 +0530
Subject: [PATCH 13/14] Fixed linter issue

---
 internal/config/hydrate_test.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/internal/config/hydrate_test.go b/internal/config/hydrate_test.go
index 81fb99a..613e3f2 100644
--- a/internal/config/hydrate_test.go
+++ b/internal/config/hydrate_test.go
@@ -110,6 +110,7 @@ func TestHydrateFile_WriteError(t *testing.T) {
 
 	err := os.Chmod(path, 0444)
 	require.NoError(t, err)
+
 	vars := map[string]string{
 		filePathVar: path,
 		"A":         "1",

From 43c00efa5abd852568d787914df8620faa494d25 Mon Sep 17 00:00:00 2001
From: Akshat Singhal <akshat.singhal@zopsmart.com>
Date: Mon, 9 Mar 2026 14:38:50 +0530
Subject: [PATCH 14/14] Added go doc for HydrateFile

---
 internal/config/hydrate.go | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/internal/config/hydrate.go b/internal/config/hydrate.go
index 4f62518..69fb91e 100644
--- a/internal/config/hydrate.go
+++ b/internal/config/hydrate.go
@@ -22,6 +22,18 @@ var (
 
 const filePathVar = "CONFIG_FILE_PATH"
 
+// HydrateFile reads the file at the path specified by the CONFIG_FILE_PATH config
+// variable, substitutes every ${VAR} placeholder with the corresponding value
+// obtained from cfg, and writes the result back to the same file.
+//
+// If CONFIG_FILE_PATH is not set (empty string), HydrateFile is a no-op and
+// returns nil. If any referenced variable is not present in the config, an
+// errMissingVars error is returned after the file has been written.
+//
+// cfg is accepted as a config.Config interface rather than as individual values
+// so that the set of variables resolved is open-ended: the file may reference
+// any variable, and HydrateFile resolves each one dynamically via cfg.Get
+// without the caller needing to know which variables the file contains.
 func HydrateFile(fs file.FileSystem, cfg config.Config) error {
 	configPath := cfg.Get(filePathVar)
 	if configPath == "" {