feat: mailfilter.transaction now only uses a temporary file to captur…

…e the mail body when it is bigger than 200KB

internal/body/body.go

@@ -0,0 +1,108 @@
+// Package body implements a write-once read-multiple [io.ReadSeekCloser] that is backed by a temporary file when too much data gets written into it.
+package body
+
+import (
+	"bytes"
+	"io"
+	"os"
+)
+
+// New creates a new Body that switches from memory-backed storage to file-backed storage
+// when more than maxMem bytes were written to it.
+//
+// If maxMem is less than 1 a temporary file gets always used.
+func New(maxMem int) *Body {
+	return &Body{maxMem: maxMem}
+}
+
+// Body is an [io.ReadSeekCloser] and [io.Writer] that starts buffering all data written to it in memory
+// but when more than a configured amount of bytes is written to it Body will switch to writing to a temporary file.
+//
+// After a call to Read or Seek no more data can be written to Body.
+// Body is an [io.Seeker] so you can read it multiple times or get the size of the Body.
+type Body struct {
+	maxMem  int
+	buf     bytes.Buffer
+	mem     *bytes.Reader
+	file    *os.File
+	reading bool
+}
+
+// Write implements the io.Writer interface.
+// Write will create a temporary file on-the-fly when you write more than the configured amount of bytes.
+func (b *Body) Write(p []byte) (n int, err error) {
+	if b.reading {
+		panic("cannot write after read")
+	}
+	if b.file != nil {
+		return b.file.Write(p)
+	}
+	n, _ = b.buf.Write(p)
+	if b.buf.Len() > b.maxMem {
+		b.file, err = os.CreateTemp("", "body-*")
+		if err != nil {
+			return
+		}
+		_, err = io.Copy(b.file, &b.buf)
+		b.buf.Reset()
+	}
+	return
+}
+
+func (b *Body) switchToReading() error {
+	if !b.reading {
+		b.reading = true
+		if b.file != nil {
+			if _, err := b.file.Seek(0, io.SeekStart); err != nil {
+				return err
+			}
+		} else {
+			b.mem = bytes.NewReader(b.buf.Bytes())
+		}
+	}
+	return nil
+}
+
+// Read implements the io.Reader interface.
+// After calling Read you cannot call Write anymore.
+func (b *Body) Read(p []byte) (n int, err error) {
+	if err := b.switchToReading(); err != nil {
+		return 0, err
+	}
+	if b.file != nil {
+
+		return b.file.Read(p)
+	}
+	return b.mem.Read(p)
+}
+
+// Close implements the io.Closer interface.
+// If a temporary file got created it will be deleted.
+func (b *Body) Close() error {
+	if b.file != nil {
+		err1 := b.file.Close()
+		err2 := os.Remove(b.file.Name())
+		if err1 != nil {
+			return err1
+		}
+		if os.IsNotExist(err2) {
+			err2 = nil
+		}
+		return err2
+	}
+	b.mem = nil
+	b.buf.Reset()
+	return nil
+}
+
+// Seek implements the io.Seeker interface.
+// After calling Seek you cannot call Write anymore.
+func (b *Body) Seek(offset int64, whence int) (int64, error) {
+	if err := b.switchToReading(); err != nil {
+		return 0, err
+	}
+	if b.file != nil {
+		return b.file.Seek(offset, whence)
+	}
+	return b.mem.Seek(offset, whence)
+}

internal/body/body_test.go

@@ -0,0 +1,158 @@
+package body
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"testing"
+)
+
+func getBody(maxMem int, data []byte) *Body {
+	b := New(maxMem)
+	_, _ = b.Write(data)
+	return b
+}
+
+func TestBody_Close(t *testing.T) {
+	fileAlreadyRemoved := getBody(2, []byte("test"))
+	_ = os.Remove(fileAlreadyRemoved.file.Name())
+	tests := []struct {
+		name    string
+		body    *Body
+		wantErr bool
+	}{
+		{"noop", getBody(10, nil), false},
+		{"mem", getBody(10, []byte("test")), false},
+		{"file", getBody(2, []byte("test")), false},
+		{"file-already-removed", fileAlreadyRemoved, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := tt.body.Close(); (err != nil) != tt.wantErr {
+				t.Errorf("Close() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestBody(t *testing.T) {
+	t.Run("mem", func(t *testing.T) {
+		b := getBody(10, []byte("test"))
+		defer b.Close()
+		_, err := b.Write([]byte("test"))
+		if err != nil {
+			t.Fatal("b.Write got error", err)
+		}
+		if b.file != nil {
+			t.Fatal("b.file needs to be nil")
+		}
+		var buf [10]byte
+		n, err := b.Read(buf[:])
+		if err != nil {
+			t.Fatal("b.Read got error", err)
+		}
+		if !bytes.Equal([]byte("testtest"), buf[:n]) {
+			t.Fatalf("b.Read got %q expected %q", buf[:n], []byte("testtest"))
+		}
+		pos, err := b.Seek(0, io.SeekStart)
+		if err != nil {
+			t.Fatal("b.Seek got error", err)
+		}
+		if pos != 0 {
+			t.Fatal("b.Seek got pos", pos)
+		}
+		n, err = b.Read(buf[:])
+		if err != nil {
+			t.Fatal("b.Read got error", err)
+		}
+		if !bytes.Equal([]byte("testtest"), buf[:n]) {
+			t.Fatalf("b.Read got %q expected %q", buf[:n], []byte("testtest"))
+		}
+	})
+	t.Run("file", func(t *testing.T) {
+		b := getBody(2, []byte("test"))
+		defer func() {
+			if b != nil {
+				b.Close()
+			}
+		}()
+		if b.file == nil {
+			t.Fatal("b.file is nil")
+		}
+		_, err := b.Write([]byte("test"))
+		if err != nil {
+			t.Fatal("b.Write got error", err)
+		}
+		var buf [10]byte
+		n, err := b.Read(buf[:])
+		if err != nil {
+			t.Fatal("b.Read got error", err)
+		}
+		if !bytes.Equal([]byte("testtest"), buf[:n]) {
+			t.Fatalf("b.Read got %q expected %q", buf[:n], []byte("testtest"))
+		}
+		pos, err := b.Seek(0, io.SeekStart)
+		if err != nil {
+			t.Fatal("b.Seek got error", err)
+		}
+		if pos != 0 {
+			t.Fatal("b.Seek got pos", pos)
+		}
+		n, err = b.Read(buf[:])
+		if err != nil {
+			t.Fatal("b.Read got error", err)
+		}
+		if !bytes.Equal([]byte("testtest"), buf[:n]) {
+			t.Fatalf("b.Read got %q expected %q", buf[:n], []byte("testtest"))
+		}
+		name := b.file.Name()
+		err = b.Close()
+		b = nil
+		if err != nil {
+			t.Fatal("b.Close got error", err)
+		}
+		_, err = os.Stat(name)
+		if err == nil || !os.IsNotExist(err) {
+			t.Fatalf("got %v expected to not find file", err)
+		}
+	})
+	t.Run("panic on Write after Read", func(t *testing.T) {
+		defer func() { _ = recover() }()
+		b := getBody(10, []byte("test"))
+		var buf [10]byte
+		_, _ = b.Read(buf[:])
+		_, _ = b.Write([]byte("test"))
+		t.Errorf("did not panic")
+	})
+	t.Run("panic on Write after Seek", func(t *testing.T) {
+		defer func() { _ = recover() }()
+		b := getBody(10, []byte("test"))
+		_, _ = b.Seek(0, io.SeekEnd)
+		_, _ = b.Write([]byte("test"))
+		t.Errorf("did not panic")
+	})
+	t.Run("temp file fail", func(t *testing.T) {
+		tmpdir := os.Getenv("TMPDIR")
+		tmp := os.Getenv("TMP")
+		_ = os.Setenv("TMPDIR", "/this does not exist")
+		_ = os.Setenv("TMP", "/this does not exist")
+		defer func() {
+			_ = os.Setenv("TMPDIR", tmpdir)
+			_ = os.Setenv("TMP", tmp)
+		}()
+		b := getBody(6, []byte("test"))
+		_, err := b.Write([]byte("test"))
+		if err == nil {
+			_ = b.Close()
+			t.Fatal("b.Write got nil error")
+		}
+	})
+	t.Run("file close fail", func(t *testing.T) {
+		b := getBody(2, []byte("test"))
+		_ = b.file.Close()
+		err := b.Close()
+		if err == nil {
+			t.Fatal("b.Close got nil error")
+		}
+	})
+}

mailfilter/transaction.go

@@ -4,10 +4,10 @@ import (
 	"bytes"
 	"context"
 	"io"
-	"os"
 	"regexp"
 
 	"github.com/d--j/go-milter"
+	"github.com/d--j/go-milter/internal/body"
 	"github.com/d--j/go-milter/internal/header"
 	"github.com/d--j/go-milter/internal/rcptto"
 	"github.com/d--j/go-milter/mailfilter/addr"
@@ -58,7 +58,7 @@ type transaction struct {
 	headers            *header.Header
 	origHeaders        *header.Header
 	enforceHeaderOrder bool
-	body               *os.File
+	body               *body.Body
 	replacementBody    io.Reader
 	queueId            string
 	hasDecision        bool
@@ -92,7 +92,6 @@ func (t *transaction) cleanup() {
 	t.closeReplacementBody()
 	if t.body != nil {
 		_ = t.body.Close()
-		_ = os.Remove(t.body.Name())
 		t.body = nil
 	}
 }
@@ -249,10 +248,7 @@ func (t *transaction) addHeader(key string, raw []byte) {
 
 func (t *transaction) addBodyChunk(chunk []byte) (err error) {
 	if t.body == nil {
-		t.body, err = os.CreateTemp("", "body-*")
-		if err != nil {
-			return
-		}
+		t.body = body.New(200 * 1024)
 	}
 	_, err = t.body.Write(chunk)
 	return