MIMEHeader: use Go's net/textproto for public interface (#297)

* MIMEHeader: use Go's net/textproto for public interface

* Use `textproto` prefix for the stdlib package where applicable

* Use inttp prefix in detect.go

builder.go

@@ -7,13 +7,13 @@ import (
 	"math/rand"
 	"mime"
 	"net/mail"
+	"net/textproto"
 	"os"
 	"path/filepath"
 	"reflect"
 	"time"
 
 	"github.com/jhillyerd/enmime/internal/stringutil"
-	"github.com/jhillyerd/enmime/internal/textproto"
 )
 
 // MailBuilder facilitates the easy construction of a MIME message.  Each manipulation method

detect.go

@@ -3,7 +3,7 @@ package enmime
 import (
 	"strings"
 
-	"github.com/jhillyerd/enmime/internal/textproto"
+	inttp "github.com/jhillyerd/enmime/internal/textproto"
 	"github.com/jhillyerd/enmime/mediatype"
 )
 
@@ -35,7 +35,7 @@ func detectMultipartMessage(root *Part, multipartWOBoundaryAsSinglepart bool) bo
 //   - Content-Disposition: attachment; filename="frog.jpg"
 //   - Content-Disposition: inline; filename="frog.jpg"
 //   - Content-Type: attachment; filename="frog.jpg"
-func detectAttachmentHeader(header textproto.MIMEHeader) bool {
+func detectAttachmentHeader(header inttp.MIMEHeader) bool {
 	mtype, params, _, _ := mediatype.Parse(header.Get(hnContentDisposition))
 	if strings.ToLower(mtype) == cdAttachment ||
 		(strings.ToLower(mtype) == cdInline && len(params) > 0) {
@@ -49,7 +49,7 @@ func detectAttachmentHeader(header textproto.MIMEHeader) bool {
 // detectTextHeader returns true, if the the MIME headers define a valid 'text/plain' or 'text/html'
 // part.  If the emptyContentTypeIsPlain argument is set to true, a missing Content-Type header will
 // result in a positive plain part detection.
-func detectTextHeader(header textproto.MIMEHeader, emptyContentTypeIsText bool) bool {
+func detectTextHeader(header inttp.MIMEHeader, emptyContentTypeIsText bool) bool {
 	ctype := header.Get(hnContentType)
 	if ctype == "" && emptyContentTypeIsText {
 		return true
@@ -67,23 +67,24 @@ func detectTextHeader(header textproto.MIMEHeader, emptyContentTypeIsText bool)
 
 // detectBinaryBody returns true if the mail header defines a binary body.
 func detectBinaryBody(root *Part) bool {
-	if detectTextHeader(root.Header, true) {
+	header := inttp.MIMEHeader(root.Header) // Use internal header methods.
+	if detectTextHeader(header, true) {
 		// It is text/plain, but an attachment.
 		// Content-Type: text/plain; name="test.csv"
 		// Content-Disposition: attachment; filename="test.csv"
 		// Check for attachment only, or inline body is marked
 		// as attachment, too.
-		mtype, _, _, _ := mediatype.Parse(root.Header.Get(hnContentDisposition))
+		mtype, _, _, _ := mediatype.Parse(header.Get(hnContentDisposition))
 		return strings.ToLower(mtype) == cdAttachment
 	}
 
-	isBin := detectAttachmentHeader(root.Header)
+	isBin := detectAttachmentHeader(header)
 	if !isBin {
 		// This must be an attachment, if the Content-Type is not
 		// 'text/plain' or 'text/html'.
 		// Example:
 		// Content-Type: application/pdf; name="doc.pdf"
-		mtype, _, _, _ := mediatype.Parse(root.Header.Get(hnContentType))
+		mtype, _, _, _ := mediatype.Parse(header.Get(hnContentType))
 		mtype = strings.ToLower(mtype)
 		if mtype != ctTextPlain && mtype != ctTextHTML {
 			return true

encode.go

@@ -6,12 +6,12 @@ import (
 	"io"
 	"mime"
 	"mime/quotedprintable"
+	"net/textproto"
 	"sort"
 	"time"
 
 	"github.com/jhillyerd/enmime/internal/coding"
 	"github.com/jhillyerd/enmime/internal/stringutil"
-	"github.com/jhillyerd/enmime/internal/textproto"
 )
 
 // b64Percent determines the percent of non-ASCII characters enmime will tolerate before switching

envelope.go

@@ -5,12 +5,13 @@ import (
 	"io"
 	"mime"
 	"net/mail"
+	"net/textproto"
 	"strings"
 	"time"
 
 	"github.com/jaytaylor/html2text"
 	"github.com/jhillyerd/enmime/internal/coding"
-	"github.com/jhillyerd/enmime/internal/textproto"
+	inttp "github.com/jhillyerd/enmime/internal/textproto"
 	"github.com/jhillyerd/enmime/mediatype"
 
 	"github.com/pkg/errors"
@@ -58,7 +59,7 @@ func (e *Envelope) GetHeaderValues(name string) []string {
 		return []string{}
 	}
 
-	rawValues := (*e.header)[textproto.CanonicalEmailMIMEHeaderKey(name)]
+	rawValues := (*e.header)[inttp.CanonicalEmailMIMEHeaderKey(name)]
 	values := make([]string, 0, len(rawValues))
 	for _, v := range rawValues {
 		values = append(values, coding.DecodeExtHeader(v))

header.go

@@ -6,11 +6,12 @@ import (
 	"fmt"
 	"mime"
 	"net/mail"
+	"net/textproto"
 	"strings"
 
 	"github.com/jhillyerd/enmime/internal/coding"
 	"github.com/jhillyerd/enmime/internal/stringutil"
-	"github.com/jhillyerd/enmime/internal/textproto"
+	inttp "github.com/jhillyerd/enmime/internal/textproto"
 	"github.com/jhillyerd/enmime/mediatype"
 
 	"github.com/pkg/errors"
@@ -123,7 +124,7 @@ func ParseMediaType(ctype string) (mtype string, params map[string]string, inval
 func readHeader(r *bufio.Reader, p *Part) (textproto.MIMEHeader, error) {
 	// buf holds the massaged output for textproto.Reader.ReadMIMEHeader()
 	buf := &bytes.Buffer{}
-	tp := textproto.NewReader(r)
+	tp := inttp.NewReader(r)
 	firstHeader := true
 line:
 	for {
@@ -139,7 +140,7 @@ line:
 		if firstSpace == 0 {
 			// Starts with space: continuation
 			buf.WriteByte(' ')
-			buf.Write(textproto.TrimBytes(s))
+			buf.Write(inttp.TrimBytes(s))
 			continue
 		}
 		if firstColon == 0 {
@@ -160,7 +161,7 @@ line:
 			// Behavior change in net/textproto package in Golang 1.20: invalid characters
 			// in header keys are no longer allowed; https://github.com/golang/go/issues/53188
 			for _, c := range s[:firstColon] {
-				if c != ' ' && !textproto.ValidEmailHeaderFieldByte(c) {
+				if c != ' ' && !inttp.ValidEmailHeaderFieldByte(c) {
 					p.addError(
 						ErrorMalformedHeader, "Header name %q contains invalid character %q", s, c)
 					continue line
@@ -173,7 +174,7 @@ line:
 				buf.Write([]byte{'\r', '\n'})
 			}
 
-			s = textproto.TrimBytes(s)
+			s = inttp.TrimBytes(s)
 			buf.Write(s)
 			firstHeader = false
 		} else {
@@ -192,9 +193,9 @@ line:
 	}
 
 	buf.Write([]byte{'\r', '\n'})
-	tr := textproto.NewReader(bufio.NewReader(buf))
+	tr := inttp.NewReader(bufio.NewReader(buf))
 	header, err := tr.ReadEmailMIMEHeader()
-	return header, errors.WithStack(err)
+	return textproto.MIMEHeader(header), errors.WithStack(err)
 }
 
 // decodeToUTF8Base64Header decodes a MIME header per RFC 2047, reencoding to =?utf-8b?

part.go

@@ -7,13 +7,14 @@ import (
 	"io"
 	"math/rand"
 	"mime/quotedprintable"
+	"net/textproto"
 	"strconv"
 	"strings"
 	"time"
 
 	"github.com/gogs/chardet"
 	"github.com/jhillyerd/enmime/internal/coding"
-	"github.com/jhillyerd/enmime/internal/textproto"
+	inttp "github.com/jhillyerd/enmime/internal/textproto"
 	"github.com/jhillyerd/enmime/mediatype"
 
 	"github.com/pkg/errors"
@@ -115,7 +116,7 @@ func (p *Part) setupHeaders(r *bufio.Reader, defaultContentType string) error {
 	if err != nil {
 		return err
 	}
-	p.Header = header
+	p.Header = textproto.MIMEHeader(header)
 	ctype := header.Get(hnContentType)
 	if ctype == "" {
 		if defaultContentType == "" {
@@ -146,8 +147,9 @@ func (p *Part) setupHeaders(r *bufio.Reader, defaultContentType string) error {
 // setupContentHeaders uses Content-Type media params and Content-Disposition headers to populate
 // the disposition, filename, and charset fields.
 func (p *Part) setupContentHeaders(mediaParams map[string]string) {
+	header := inttp.MIMEHeader(p.Header)
 	// Determine content disposition, filename, character set.
-	disposition, dparams, _, err := mediatype.Parse(p.Header.Get(hnContentDisposition))
+	disposition, dparams, _, err := mediatype.Parse(header.Get(hnContentDisposition))
 	if err == nil {
 		// Disposition is optional
 		p.Disposition = disposition
@@ -269,12 +271,13 @@ func (p *Part) convertFromStatedCharset(r io.Reader) io.Reader {
 // placing the result into Part.Content.  IO errors will be returned immediately; other errors
 // and warnings will be added to Part.Errors.
 func (p *Part) decodeContent(r io.Reader, readPartErrorPolicy ReadPartErrorPolicy) error {
+	header := inttp.MIMEHeader(p.Header)
 	// contentReader will point to the end of the content decoding pipeline.
 	contentReader := r
 	// b64cleaner aggregates errors, must maintain a reference to it to get them later.
 	var b64cleaner *coding.Base64Cleaner
 	// Build content decoding reader.
-	encoding := p.Header.Get(hnContentEncoding)
+	encoding := header.Get(hnContentEncoding)
 	validEncoding := true
 	switch strings.ToLower(encoding) {
 	case cteQuotedPrintable: