add formbind package for nested struct form data binding

formbind/README.md

@@ -0,0 +1,120 @@
+# formbind
+
+A standalone library for binding nested form data to Go structs. This library provides advanced form binding capabilities with support for nested structures, arrays, and pointer fields.
+
+## Features
+
+- **Nested Struct Binding**: Bind deeply nested structures from form data
+- **Array Support**: Handle array notation with indices (e.g., `items[0].name`)
+- **Pointer Field Support**: Automatically handle pointer fields and nil checks
+- **Dot Notation**: Support for nested field access using dot notation
+- **Sparse Arrays**: Handle non-sequential array indices gracefully
+- **Zero Dependencies**: No external dependencies beyond Go standard library
+
+## Installation
+
+```bash
+go get github.com/labstack/echo-contrib/formbind
+```
+
+## Usage
+
+```go
+package main
+
+import (
+    "fmt"
+    "net/url"
+
+    "github.com/labstack/echo-contrib/formbind"
+)
+
+type Person struct {
+    Name  string `form:"name"`
+    Email string `form:"email"`
+}
+
+type Team struct {
+    Name    string   `form:"name"`
+    Members []Person `form:"members"`
+}
+
+func main() {
+    // Parse form data
+    formData := url.Values{
+        "name":               {"Engineering Team"},
+        "members[0].name":    {"Alice"},
+        "members[0].email":   {"alice@example.com"},
+        "members[1].name":    {"Bob"},
+        "members[1].email":   {"bob@example.com"},
+    }
+
+    var team Team
+    err := formbind.Bind(&team, formData)
+    if err != nil {
+        panic(err)
+    }
+
+    fmt.Printf("%+v\n", team)
+    // Output: {Name:Engineering Team Members:[{Name:Alice Email:alice@example.com} {Name:Bob Email:bob@example.com}]}
+}
+```
+
+## API Reference
+
+### formbind.Bind
+
+```go
+func Bind(dst interface{}, data url.Values) error
+```
+
+Binds form data to the destination struct. The destination must be a pointer to a struct.
+
+### Supported Field Types
+
+- `string`
+- `int`, `int8`, `int16`, `int32`, `int64`
+- `uint`, `uint8`, `uint16`, `uint32`, `uint64`
+- `float32`, `float64`
+- `bool`
+- `time.Time` (with custom time format support)
+- Slices of above types
+- Nested structs
+- Pointers to any of the above types
+
+### Form Tags
+
+The library uses the `form` tag to map form fields to struct fields:
+
+```go
+type User struct {
+    Name  string `form:"name"`
+    Email string `form:"email_address"`
+}
+```
+
+If no `form` tag is provided, the field name is used (case-insensitive matching).
+
+## Error Handling
+
+The library returns descriptive errors for common issues:
+
+```go
+var data FormData
+err := formbind.Bind(&data, formValues)
+if err != nil {
+    // Handle specific error types
+    switch err.(type) {
+    case *formbind.BindError:
+        // Field-specific binding error
+    case *formbind.ParseError:
+        // Value parsing error
+    default:
+        // Other errors
+    }
+}
+```
+
+## Origin
+
+This library is based on the nested form binding implementation proposed in [Echo PR #2834](https://github.com/labstack/echo/pull/2834), extracted as a standalone library for broader use.