lib/http: refactoring "multipart/form-data" parameters in ClientRequest

Previously, ClientRequest with type RequestTypeMultipartForm pass the
type "map[string][]byte" in Params.
This type hold the file upload, where key is the file name and []byte is
content of file.
Unfortunately, this model does not correct because a
"multipart/form-data" can contains different field name and file name,
for example

  --boundary
  Content-Disposition: form-data; name="field0"; filename="file0"
  Content-Type: application/octet-stream

  <Content of file0>

This changes fix this by changing the parameter type for
RequestTypeMultipartForm to [*multipart.Form], which affect several
functions including [Client.PutFormData] and [GenerateFormData].

We also add new function [CreateMultipartFileHeader] to help creating
[multipart.FileHeader] from raw bytes, that can be assigned to
[*multipart.Form].

6 files changed, 295 insertions, 57 deletions

diff --git a/lib/http/client.go b/lib/http/client.go
index 10ee1a2c..751b1de3 100644
--- a/lib/http/client.go
+++ b/lib/http/client.go
@@ -21,7 +21,6 @@ import (
 	"net"
 	"net/http"
 	"path"
-	"sort"
 	"strings"
 	"time"
 
@@ -193,7 +192,7 @@ out:
 //   - If Type is [RequestTypeForm] and Params is [url.Values] it
 //     will be send as URL encoded in the body.
 //   - If Type is [RequestTypeMultipartForm] and Params type is
-//     map[string][]byte, then it will send as multipart form in the
+//     [*multipart.Form], then it will send as multipart form in the
 //     body.
 //   - If Type is [RequestTypeJSON] and Params is not nil, the Params
 //     will be encoded as JSON in the body.
@@ -224,15 +223,15 @@ func (client *Client) GenerateHTTPRequest(req ClientRequest) (httpReq *http.Requ
 
 	case RequestTypeMultipartForm:
 		var (
-			paramsAsMultipart map[string][]byte
-			ok                bool
+			mpform *multipart.Form
+			ok     bool
 		)
 
-		paramsAsMultipart, ok = req.Params.(map[string][]byte)
+		mpform, ok = req.Params.(*multipart.Form)
 		if ok {
 			var strBody string
 
-			contentType, strBody, err = GenerateFormData(paramsAsMultipart)
+			contentType, strBody, err = GenerateFormData(mpform)
 			if err != nil {
 				return nil, fmt.Errorf(`%s: %w`, logp, err)
 			}
@@ -331,7 +330,7 @@ func (client *Client) PostFormData(req ClientRequest) (res *ClientResponse, err
 	var (
 		logp = `PostFormData`
 
-		params map[string][]byte
+		params *multipart.Form
 	)
 
 	req.contentType = req.Type.String()
@@ -405,8 +404,9 @@ func (client *Client) PutForm(req ClientRequest) (*ClientResponse, error) {
 // "multipart/form-data".
 func (client *Client) PutFormData(req ClientRequest) (res *ClientResponse, err error) {
 	var (
-		logp   = `PutFormData`
-		params map[string][]byte
+		logp = `PutFormData`
+
+		params *multipart.Form
 	)
 
 	req.contentType = req.Type.String()
@@ -574,43 +574,3 @@ func (client *Client) uncompress(res *http.Response, body []byte) (
 
 	return out, err
 }
-
-// GenerateFormData generate multipart/form-data body from params.
-func GenerateFormData(params map[string][]byte) (contentType, body string, err error) {
-	var (
-		sb      = new(strings.Builder)
-		w       = multipart.NewWriter(sb)
-		listKey = make([]string, 0, len(params))
-
-		k string
-	)
-	for k = range params {
-		listKey = append(listKey, k)
-	}
-	sort.Strings(listKey)
-
-	var (
-		part io.Writer
-		v    []byte
-	)
-	for _, k = range listKey {
-		part, err = w.CreateFormField(k)
-		if err != nil {
-			return "", "", err
-		}
-		v = params[k]
-		_, err = part.Write(v)
-		if err != nil {
-			return "", "", err
-		}
-	}
-
-	err = w.Close()
-	if err != nil {
-		return "", "", err
-	}
-
-	contentType = w.FormDataContentType()
-
-	return contentType, sb.String(), nil
-}
diff --git a/lib/http/client_example_test.go b/lib/http/client_example_test.go
index 7b72cba1..22b24285 100644
--- a/lib/http/client_example_test.go
+++ b/lib/http/client_example_test.go
@@ -4,6 +4,7 @@ import (
 	"crypto/rand"
 	"fmt"
 	"log"
+	"mime/multipart"
 	"strings"
 
 	libhttp "git.sr.ht/~shulhan/pakakeh.go/lib/http"
@@ -15,9 +16,11 @@ func ExampleGenerateFormData() {
 	// NOTE: do not do this on real code.
 	rand.Reader = mock.NewRandReader([]byte(`randomseed`))
 
-	var data = map[string][]byte{
-		`name`: []byte(`test.txt`),
-		`size`: []byte(`42`),
+	var data = &multipart.Form{
+		Value: map[string][]string{
+			`name`: []string{`test.txt`},
+			`size`: []string{`42`},
+		},
 	}
 
 	var (
diff --git a/lib/http/client_request.go b/lib/http/client_request.go
index 454aeae1..55cf3ab3 100644
--- a/lib/http/client_request.go
+++ b/lib/http/client_request.go
@@ -10,6 +10,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"mime/multipart"
 	"net/http"
 	"net/url"
 	"strings"
@@ -111,7 +112,7 @@ func (creq *ClientRequest) toHTTPRequest(client *Client) (httpReq *http.Request,
 			}
 
 		case RequestTypeMultipartForm:
-			paramsAsMultipart, ok := creq.Params.(map[string][]byte)
+			paramsAsMultipart, ok := creq.Params.(*multipart.Form)
 			if ok {
 				contentType, strBody, err = GenerateFormData(paramsAsMultipart)
 				if err != nil {
@@ -170,16 +171,16 @@ func (creq *ClientRequest) paramsAsURLEncoded() string {
 	return params.Encode()
 }
 
-// paramsAsMultipart convert the Params as "map[string][]byte" and return the
-// content type and body.
-func (creq *ClientRequest) paramsAsMultipart() (params map[string][]byte) {
+// paramsAsMultipart convert the Params as [*multipart.Form] or nil if its
+// empty.
+func (creq *ClientRequest) paramsAsMultipart() (params *multipart.Form) {
 	if creq.Params == nil {
 		return nil
 	}
 
 	var ok bool
 
-	params, ok = creq.Params.(map[string][]byte)
+	params, ok = creq.Params.(*multipart.Form)
 	if !ok {
 		return nil
 	}
diff --git a/lib/http/multipart_form.go b/lib/http/multipart_form.go
new file mode 100644
index 00000000..bd535cfe
--- /dev/null
+++ b/lib/http/multipart_form.go
@@ -0,0 +1,168 @@
+// Copyright 2024, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"mime/multipart"
+	"sort"
+	"strings"
+)
+
+// CreateMultipartFileHeader create [multipart.FileHeader] from raw content
+// with optional filename.
+func CreateMultipartFileHeader(filename string, content []byte) (fh *multipart.FileHeader, err error) {
+	var (
+		logp      = `NewMultipartFormFile`
+		boundary  = `__boundary__`
+		fieldname = `__fieldname__`
+
+		buf bytes.Buffer
+	)
+
+	var wrt = multipart.NewWriter(&buf)
+
+	err = wrt.SetBoundary(boundary)
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	var formfile io.Writer
+
+	formfile, err = wrt.CreateFormFile(fieldname, filename)
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	_, err = formfile.Write(content)
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	err = wrt.Close()
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	var (
+		rdr = multipart.NewReader(&buf, boundary)
+
+		form *multipart.Form
+	)
+
+	form, err = rdr.ReadForm(0)
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	var (
+		listFH []*multipart.FileHeader
+		ok     bool
+	)
+
+	listFH, ok = form.File[fieldname]
+	if !ok {
+		return nil, fmt.Errorf(`%s: missing generated file %s`, logp, filename)
+	}
+	if len(listFH) == 0 {
+		return nil, fmt.Errorf(`%s: empty generated FileHeader`, logp)
+	}
+
+	fh = listFH[0]
+
+	return fh, nil
+}
+
+// GenerateFormData generate "multipart/form-data" body from mpform.
+func GenerateFormData(mpform *multipart.Form) (contentType, body string, err error) {
+	if mpform == nil {
+		return ``, ``, nil
+	}
+
+	var (
+		logp    = `GenerateFormData`
+		sb      = new(strings.Builder)
+		w       = multipart.NewWriter(sb)
+		listKey = make([]string, 0, len(mpform.File))
+
+		k string
+	)
+
+	// Generate files part.
+
+	for k = range mpform.File {
+		listKey = append(listKey, k)
+	}
+	sort.Strings(listKey)
+
+	var (
+		listFH  []*multipart.FileHeader
+		fh      *multipart.FileHeader
+		part    io.Writer
+		file    multipart.File
+		content []byte
+	)
+	for k, listFH = range mpform.File {
+		for _, fh = range listFH {
+			part, err = w.CreateFormFile(k, fh.Filename)
+			if err != nil {
+				return ``, ``, fmt.Errorf(`%s: %w`, logp, err)
+			}
+
+			file, err = fh.Open()
+			if err != nil {
+				return ``, ``, fmt.Errorf(`%s: %w`, logp, err)
+			}
+
+			content, err = io.ReadAll(file)
+			if err != nil {
+				return ``, ``, fmt.Errorf(`%s: %w`, logp, err)
+			}
+
+			_, err = part.Write(content)
+			if err != nil {
+				return ``, ``, fmt.Errorf(`%s: %w`, logp, err)
+			}
+		}
+	}
+
+	// Generate values part.
+
+	listKey = listKey[:0]
+	for k = range mpform.Value {
+		listKey = append(listKey, k)
+	}
+	sort.Strings(listKey)
+
+	var (
+		listValue []string
+		v         string
+	)
+	for _, k = range listKey {
+		listValue = mpform.Value[k]
+		for _, v = range listValue {
+			part, err = w.CreateFormField(k)
+			if err != nil {
+				return ``, ``, err
+			}
+
+			_, err = part.Write([]byte(v))
+			if err != nil {
+				return ``, ``, err
+			}
+		}
+	}
+
+	err = w.Close()
+	if err != nil {
+		return ``, ``, err
+	}
+
+	contentType = w.FormDataContentType()
+
+	return contentType, sb.String(), nil
+}
diff --git a/lib/http/multipart_form_test.go b/lib/http/multipart_form_test.go
new file mode 100644
index 00000000..8562acc7
--- /dev/null
+++ b/lib/http/multipart_form_test.go
@@ -0,0 +1,84 @@
+// Copyright 2024, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http
+
+import (
+	"crypto/rand"
+	"mime/multipart"
+	"strings"
+	"testing"
+
+	"git.sr.ht/~shulhan/pakakeh.go/lib/test"
+	"git.sr.ht/~shulhan/pakakeh.go/lib/test/mock"
+)
+
+func TestGenerateFormData(t *testing.T) {
+	type testcase struct {
+		form           multipart.Form
+		tagOutput      string
+		field2filename map[string]string
+	}
+
+	rand.Reader = mock.NewRandReader([]byte(`randomseed`))
+
+	var (
+		tdata *test.Data
+		err   error
+	)
+	tdata, err = test.LoadData(`testdata/GenerateFormData_test.txt`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var listcase = []testcase{{
+		form: multipart.Form{
+			Value: map[string][]string{
+				`field1`: []string{`value1`, `value1.1`},
+			},
+			File: map[string][]*multipart.FileHeader{},
+		},
+		field2filename: map[string]string{
+			`field0`: `file0`,
+		},
+		tagOutput: `file0`,
+	}}
+
+	var (
+		tcase  testcase
+		listFH []*multipart.FileHeader
+		fh     *multipart.FileHeader
+
+		fieldname      string
+		filename       string
+		gotContentType string
+		gotBody        string
+		tag            string
+	)
+
+	for _, tcase = range listcase {
+		for fieldname, filename = range tcase.field2filename {
+			fh, err = CreateMultipartFileHeader(filename, tdata.Input[filename])
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			listFH = tcase.form.File[fieldname]
+			listFH = append(listFH, fh)
+			tcase.form.File[fieldname] = listFH
+		}
+
+		gotContentType, gotBody, err = GenerateFormData(&tcase.form)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		tag = tcase.tagOutput + `.ContentType`
+		test.Assert(t, tag, string(tdata.Output[tag]), gotContentType)
+
+		gotBody = strings.ReplaceAll(gotBody, "\r\n", "\n")
+		tag = tcase.tagOutput + `.Body`
+		test.Assert(t, tag, string(tdata.Output[tag]), gotBody)
+	}
+}
diff --git a/lib/http/testdata/GenerateFormData_test.txt b/lib/http/testdata/GenerateFormData_test.txt
new file mode 100644
index 00000000..b209e07f
--- /dev/null
+++ b/lib/http/testdata/GenerateFormData_test.txt
@@ -0,0 +1,22 @@
+
+>>> file0
+Content of file0.
+
+<<< file0.ContentType
+multipart/form-data; boundary=616e646f6d73656564616e646f6d73656564616e646f6d73656564616e64
+
+<<< file0.Body
+--616e646f6d73656564616e646f6d73656564616e646f6d73656564616e64
+Content-Disposition: form-data; name="field0"; filename="file0"
+Content-Type: application/octet-stream
+
+Content of file0.
+--616e646f6d73656564616e646f6d73656564616e646f6d73656564616e64
+Content-Disposition: form-data; name="field1"
+
+value1
+--616e646f6d73656564616e646f6d73656564616e646f6d73656564616e64
+Content-Disposition: form-data; name="field1"
+
+value1.1
+--616e646f6d73656564616e646f6d73656564616e646f6d73656564616e64--