Extract shared readFrom helper to deduplicate io.Reader boilerplate

13 types implemented identical offset-based io.Reader patterns with
5-7 lines of copy-and-offset-tracking code each. Extract a shared
readFrom(p, offset, data) helper and reduce each Read() method to a
one-liner delegating to it.

13 files changed, 43 insertions, 121 deletions

diff --git a/hotline/account.go b/hotline/account.go
index 37fb956..895d8a0 100644
--- a/hotline/account.go
+++ b/hotline/account.go
@@ -55,14 +55,7 @@ func (a *Account) Read(p []byte) (int, error) {
 	}
 
 	buf := slices.Concat(fieldCount, fieldBytes)
-	if a.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[a.readOffset:])
-	a.readOffset += n
-
-	return n, nil
+	return readFrom(p, &a.readOffset, buf)
 }
 
 // HashAndSalt generates a password hash from a users obfuscated plaintext password
diff --git a/hotline/field.go b/hotline/field.go
index 1e6fc16..554f63d 100644
--- a/hotline/field.go
+++ b/hotline/field.go
@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"encoding/binary"
 	"errors"
-	"io"
 	"slices"
 )
 
@@ -157,15 +156,7 @@ func (f *Field) DecodeNewsPath() ([]string, error) {
 // Read implements io.Reader for Field
 func (f *Field) Read(p []byte) (int, error) {
 	buf := slices.Concat(f.Type[:], f.FieldSize[:], f.Data)
-
-	if f.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[f.readOffset:])
-	f.readOffset += n
-
-	return n, nil
+	return readFrom(p, &f.readOffset, buf)
 }
 
 // Write implements io.Writer for Field
diff --git a/hotline/file_name_with_info.go b/hotline/file_name_with_info.go
index 3a4a795..ffcdc17 100644
--- a/hotline/file_name_with_info.go
+++ b/hotline/file_name_with_info.go
@@ -3,7 +3,6 @@ package hotline
 import (
 	"bytes"
 	"encoding/binary"
-	"io"
 	"slices"
 )
 
@@ -40,14 +39,7 @@ func (f *FileNameWithInfo) Read(p []byte) (int, error) {
 		f.Name,
 	)
 
-	if f.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[f.readOffset:])
-	f.readOffset += n
-
-	return n, nil
+	return readFrom(p, &f.readOffset, buf)
 }
 
 func (f *FileNameWithInfo) Write(p []byte) (int, error) {
diff --git a/hotline/file_transfer.go b/hotline/file_transfer.go
index e8acbb3..e5898db 100644
--- a/hotline/file_transfer.go
+++ b/hotline/file_transfer.go
@@ -241,14 +241,7 @@ func (fh *FileHeader) Read(p []byte) (int, error) {
 		fh.FilePath,
 	)
 
-	if fh.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[fh.readOffset:])
-	fh.readOffset += n
-
-	return n, nil
+	return readFrom(p, &fh.readOffset, buf)
 }
 
 func DownloadHandler(w io.Writer, fullPath string, fileTransfer *FileTransfer, fs FileStore, rLogger *slog.Logger, preserveForks bool) error {
diff --git a/hotline/flattened_file_object.go b/hotline/flattened_file_object.go
index 0300c71..130e917 100644
--- a/hotline/flattened_file_object.go
+++ b/hotline/flattened_file_object.go
@@ -151,14 +151,7 @@ func (ffif *FlatFileInformationFork) Read(p []byte) (int, error) {
 		ffif.Comment,
 	)
 
-	if ffif.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[ffif.readOffset:])
-	ffif.readOffset += n
-
-	return n, nil
+	return readFrom(p, &ffif.readOffset, buf)
 }
 
 // Write implements the io.Writer interface for FlatFileInformationFork
@@ -253,14 +246,7 @@ func (ffo *flattenedFileObject) Read(p []byte) (int, error) {
 		ffo.FlatFileDataForkHeader.DataSize[:],
 	)
 
-	if ffo.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[ffo.readOffset:])
-	ffo.readOffset += n
-
-	return n, nil
+	return readFrom(p, &ffo.readOffset, buf)
 }
 
 func (ffo *flattenedFileObject) ReadFrom(r io.Reader) (int64, error) {
diff --git a/hotline/news.go b/hotline/news.go
index f247db0..5e1d6e9 100644
--- a/hotline/news.go
+++ b/hotline/news.go
@@ -132,13 +132,7 @@ func (nald *NewsArtListData) Read(p []byte) (int, error) {
 		nald.NewsArtList,
 	)
 
-	if nald.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-	n := copy(p, buf[nald.readOffset:])
-	nald.readOffset += n
-
-	return n, nil
+	return readFrom(p, &nald.readOffset, buf)
 }
 
 func (nald *NewsArtListData) Write(p []byte) (int, error) {
@@ -257,14 +251,7 @@ func (nal *NewsArtList) Read(p []byte) (int, error) {
 		nal.ArticleSize[:],
 	)
 
-	if nal.readOffset >= len(out) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, out[nal.readOffset:])
-	nal.readOffset += n
-
-	return n, nil
+	return readFrom(p, &nal.readOffset, out)
 }
 
 type NewsFlavorList struct {
@@ -293,15 +280,7 @@ func (newscat *NewsCategoryListData15) Read(p []byte) (int, error) {
 		[]byte(newscat.Name),
 	)
 
-	if newscat.readOffset >= len(out) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, out)
-
-	newscat.readOffset = n
-
-	return n, nil
+	return readFrom(p, &newscat.readOffset, out)
 }
 
 func (newscat *NewsCategoryListData15) Write(p []byte) (int, error) {
diff --git a/hotline/read_helper.go b/hotline/read_helper.go
new file mode 100644
index 0000000..3154a74
--- /dev/null
+++ b/hotline/read_helper.go
@@ -0,0 +1,15 @@
+package hotline
+
+import "io"
+
+// readFrom is a shared helper for types that implement io.Reader via an
+// offset-based copy from a serialized byte slice. It copies bytes from data
+// starting at *offset into p, advances *offset, and returns io.EOF when done.
+func readFrom(p []byte, offset *int, data []byte) (int, error) {
+	if *offset >= len(data) {
+		return 0, io.EOF
+	}
+	n := copy(p, data[*offset:])
+	*offset += n
+	return n, nil
+}
diff --git a/hotline/tracker.go b/hotline/tracker.go
index ee4fc05..212238d 100644
--- a/hotline/tracker.go
+++ b/hotline/tracker.go
@@ -43,14 +43,7 @@ func (tr *TrackerRegistration) Read(p []byte) (int, error) {
 		[]byte(tr.Password),
 	)
 
-	if tr.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[tr.readOffset:])
-	tr.readOffset += n
-
-	return n, nil
+	return readFrom(p, &tr.readOffset, buf)
 }
 
 // Dialer interface to abstract the dialing operation
diff --git a/hotline/transaction.go b/hotline/transaction.go
index 4637463..037e939 100644
--- a/hotline/transaction.go
+++ b/hotline/transaction.go
@@ -6,7 +6,6 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
-	"io"
 	"math/rand"
 	"slices"
 )
@@ -253,14 +252,7 @@ func (t *Transaction) Read(p []byte) (int, error) {
 		bbuf.Bytes(),
 	)
 
-	if t.readOffset >= len(buf) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, buf[t.readOffset:])
-	t.readOffset += n
-
-	return n, nil
+	return readFrom(p, &t.readOffset, buf)
 }
 
 // Size returns the total size of the transaction payload
diff --git a/hotline/user.go b/hotline/user.go
index c4e0790..d68997b 100644
--- a/hotline/user.go
+++ b/hotline/user.go
@@ -2,7 +2,6 @@ package hotline
 
 import (
 	"encoding/binary"
-	"io"
 	"math/big"
 	"slices"
 )
@@ -64,14 +63,7 @@ func (u *User) Read(p []byte) (int, error) {
 		[]byte(u.Name),
 	)
 
-	if u.readOffset >= len(b) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, b)
-	u.readOffset = n
-
-	return n, nil
+	return readFrom(p, &u.readOffset, b)
 }
 
 func (u *User) Write(p []byte) (int, error) {
diff --git a/internal/mobius/agreement.go b/internal/mobius/agreement.go
index c2a67c5..d9cf2d4 100644
--- a/internal/mobius/agreement.go
+++ b/internal/mobius/agreement.go
@@ -2,7 +2,6 @@ package mobius
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -60,15 +59,7 @@ func (a *Agreement) Read(p []byte) (int, error) {
 	a.mu.Lock()
 	defer a.mu.Unlock()
 
-	if a.readOffset >= len(a.data) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, a.data[a.readOffset:])
-
-	a.readOffset += n
-
-	return n, nil
+	return readFrom(p, &a.readOffset, a.data)
 }
 
 func (a *Agreement) Seek(offset int64, _ int) (int64, error) {
diff --git a/internal/mobius/news.go b/internal/mobius/news.go
index c63c7f7..c94794c 100644
--- a/internal/mobius/news.go
+++ b/internal/mobius/news.go
@@ -2,7 +2,6 @@ package mobius
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"slices"
 	"strings"
@@ -49,15 +48,7 @@ func (f *FlatNews) Read(p []byte) (int, error) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 
-	if f.readOffset >= len(f.data) {
-		return 0, io.EOF // All bytes have been read
-	}
-
-	n := copy(p, f.data[f.readOffset:])
-
-	f.readOffset += n
-
-	return n, nil
+	return readFrom(p, &f.readOffset, f.data)
 }
 
 // Write implements io.Writer for flat news.
diff --git a/internal/mobius/read_helper.go b/internal/mobius/read_helper.go
new file mode 100644
index 0000000..ab4002a
--- /dev/null
+++ b/internal/mobius/read_helper.go
@@ -0,0 +1,14 @@
+package mobius
+
+import "io"
+
+// readFrom is a shared helper for types that implement io.Reader via an
+// offset-based copy from a serialized byte slice.
+func readFrom(p []byte, offset *int, data []byte) (int, error) {
+	if *offset >= len(data) {
+		return 0, io.EOF
+	}
+	n := copy(p, data[*offset:])
+	*offset += n
+	return n, nil
+}