feat: add GetRequestBody() method for reusable request body access

- Add Context.GetRequestBody() method that caches request body bytes
- Allows multiple reads of request body without consumption
- Integrates with existing ShouldBindBodyWith* caching mechanism
- Includes comprehensive tests and usage examples
- Addresses issue #1974: Wrap Request.Body for reuse by Gin, middlewares and app code

context.go

@@ -1080,6 +1080,33 @@ func (c *Context) GetRawData() ([]byte, error) {
 	return io.ReadAll(c.Request.Body)
 }
 
+// GetRequestBody returns the request body as bytes, caching it for reuse.
+// This allows the body to be read multiple times without being consumed.
+// Returns an error if the body cannot be read or if it's nil.
+func (c *Context) GetRequestBody() ([]byte, error) {
+	if c.Request.Body == nil {
+		return nil, errors.New("cannot read nil body")
+	}
+
+	// Check if body is already cached
+	if cb, ok := c.Get(BodyBytesKey); ok {
+		if cbb, ok := cb.([]byte); ok {
+			return cbb, nil
+		}
+	}
+
+	// Read and cache the body
+	body, err := io.ReadAll(c.Request.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	// Cache the body for future use
+	c.Set(BodyBytesKey, body)
+
+	return body, nil
+}
+
 // SetSameSite with cookie
 func (c *Context) SetSameSite(samesite http.SameSite) {
 	c.sameSite = samesite

context_test.go

@@ -2872,6 +2872,105 @@ func TestContextGetRawData(t *testing.T) {
 	assert.Equal(t, "Fetch binary post data", string(data))
 }
 
+func TestContextGetRequestBody(t *testing.T) {
+	// Test basic functionality
+	t.Run("basic functionality", func(t *testing.T) {
+		c, _ := CreateTestContext(httptest.NewRecorder())
+		bodyContent := "test request body data"
+		body := strings.NewReader(bodyContent)
+		c.Request, _ = http.NewRequest(http.MethodPost, "/", body)
+
+		data, err := c.GetRequestBody()
+		require.NoError(t, err)
+		assert.Equal(t, bodyContent, string(data))
+	})
+
+	// Test multiple calls return cached data
+	t.Run("multiple calls return cached data", func(t *testing.T) {
+		c, _ := CreateTestContext(httptest.NewRecorder())
+		bodyContent := "reusable request body"
+		body := strings.NewReader(bodyContent)
+		c.Request, _ = http.NewRequest(http.MethodPost, "/", body)
+
+		// First call
+		data1, err1 := c.GetRequestBody()
+		require.NoError(t, err1)
+		assert.Equal(t, bodyContent, string(data1))
+
+		// Second call should return cached data
+		data2, err2 := c.GetRequestBody()
+		require.NoError(t, err2)
+		assert.Equal(t, bodyContent, string(data2))
+
+		// Third call should also return cached data
+		data3, err3 := c.GetRequestBody()
+		require.NoError(t, err3)
+		assert.Equal(t, bodyContent, string(data3))
+
+		// All calls should return the same data
+		assert.Equal(t, data1, data2)
+		assert.Equal(t, data2, data3)
+	})
+
+	// Test nil body error
+	t.Run("nil body error", func(t *testing.T) {
+		c, _ := CreateTestContext(httptest.NewRecorder())
+		c.Request, _ = http.NewRequest(http.MethodPost, "/", nil)
+		c.Request.Body = nil
+
+		data, err := c.GetRequestBody()
+		assert.Error(t, err)
+		assert.Nil(t, data)
+		assert.Contains(t, err.Error(), "cannot read nil body")
+	})
+
+	// Test empty body
+	t.Run("empty body", func(t *testing.T) {
+		c, _ := CreateTestContext(httptest.NewRecorder())
+		body := strings.NewReader("")
+		c.Request, _ = http.NewRequest(http.MethodPost, "/", body)
+
+		data, err := c.GetRequestBody()
+		require.NoError(t, err)
+		assert.Equal(t, "", string(data))
+		assert.Equal(t, 0, len(data))
+	})
+
+	// Test large body
+	t.Run("large body", func(t *testing.T) {
+		c, _ := CreateTestContext(httptest.NewRecorder())
+		largeContent := strings.Repeat("large body content ", 1000)
+		body := strings.NewReader(largeContent)
+		c.Request, _ = http.NewRequest(http.MethodPost, "/", body)
+
+		data, err := c.GetRequestBody()
+		require.NoError(t, err)
+		assert.Equal(t, largeContent, string(data))
+		assert.Equal(t, len(largeContent), len(data))
+	})
+
+	// Test integration with ShouldBindBodyWith
+	t.Run("integration with ShouldBindBodyWith", func(t *testing.T) {
+		c, _ := CreateTestContext(httptest.NewRecorder())
+		jsonBody := `{"name":"test","value":123}`
+		body := strings.NewReader(jsonBody)
+		c.Request, _ = http.NewRequest(http.MethodPost, "/", body)
+		c.Request.Header.Set("Content-Type", "application/json")
+
+		// Get body first
+		bodyData, err := c.GetRequestBody()
+		require.NoError(t, err)
+		assert.Equal(t, jsonBody, string(bodyData))
+
+		// ShouldBindBodyWith should still work and reuse cached body
+		var jsonData map[string]interface{}
+		err = c.ShouldBindBodyWithJSON(&jsonData)
+		require.NoError(t, err)
+		assert.Equal(t, "test", jsonData["name"])
+		assert.Equal(t, float64(123), jsonData["value"])
+	})
+}
+
 func TestContextRenderDataFromReader(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := CreateTestContext(w)

examples/get_request_body_example.go

@@ -0,0 +1,86 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+func main() {
+	r := gin.Default()
+
+	// Example middleware that reads the request body
+	r.Use(func(c *gin.Context) {
+		// Get the request body - this can be called multiple times
+		body, err := c.GetRequestBody()
+		if err != nil {
+			c.AbortWithError(http.StatusBadRequest, err)
+			return
+		}
+
+		// Log the body length for demonstration
+		fmt.Printf("Middleware: Request body length: %d bytes\n", len(body))
+
+		// Store body in context for use by handlers
+		c.Set("rawBody", body)
+		c.Next()
+	})
+
+	// Handler that also reads the body
+	r.POST("/echo", func(c *gin.Context) {
+		// Get the body again - this will use the cached version
+		body, err := c.GetRequestBody()
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+
+		// Also get the body that was stored by middleware
+		storedBody, exists := c.Get("rawBody")
+		if !exists {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "body not found in context"})
+			return
+		}
+
+		// Both should be identical
+		if string(body) != string(storedBody.([]byte)) {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "bodies don't match"})
+			return
+		}
+
+		c.JSON(http.StatusOK, gin.H{
+			"message": "Body received and cached successfully",
+			"body":    string(body),
+			"length":  len(body),
+		})
+	})
+
+	// Handler that uses binding after GetRequestBody
+	r.POST("/bind-after-body", func(c *gin.Context) {
+		// First bind to a struct - this caches the body
+		var jsonData map[string]interface{}
+		if err := c.ShouldBindBodyWithJSON(&jsonData); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+
+		// Then get the raw body - this will use the cached version
+		rawBody, err := c.GetRequestBody()
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+
+		c.JSON(http.StatusOK, gin.H{
+			"raw_body": string(rawBody),
+			"parsed_data": jsonData,
+		})
+	})
+
+	fmt.Println("Server starting on :9090")
+	fmt.Println("Try: curl -X POST -d 'hello world' http://localhost:9090/echo")
+	fmt.Println("Or: curl -X POST -H 'Content-Type: application/json' -d '{\"name\":\"test\"}' http://localhost:9090/bind-after-body")
+
+	r.Run(":9090")
+}