docs: add CLAUDE.md

If the C library supports these random functions, use them directly
instead of reading the /dev/urandom file.  This makes life easier on
platforms that don't have /dev/urandom (like WASM).

.github/workflows/ci.yml

@@ -8,11 +8,11 @@ jobs:
 
     strategy:
       matrix:
-        os: [macos-latest, ubuntu-20.04, ubuntu-22.04]
+        os: [macos-latest, ubuntu-22.04, ubuntu-24.04]
         crypto: [auto]
         include:
           - crypto: nettle
-            os: ubuntu-20.04
+            os: ubuntu-22.04
         
 
     steps:
@@ -20,7 +20,7 @@ jobs:
 
     - name: "setup linux build environment"
       if: ${{ startsWith(matrix.os, 'ubuntu') }}
-      run: sudo apt install -y protobuf-compiler libprotobuf-dev libutempter-dev autoconf automake nettle-dev
+      run: sudo apt update && sudo apt install -y protobuf-compiler libprotobuf-dev libutempter-dev autoconf automake nettle-dev
 
     - name: "setup macos build environment"
       if: ${{ startsWith(matrix.os, 'macos') }}

.github/workflows/release.yml

@@ -59,7 +59,7 @@ jobs:
 
     - name: "setup linux build environment"
       if: ${{ startsWith(matrix.os, 'ubuntu') }}
-      run: sudo apt install -y protobuf-compiler libprotobuf-dev libutempter-dev autoconf automake nettle-dev
+      run: sudo apt update && sudo apt install -y protobuf-compiler libprotobuf-dev libutempter-dev autoconf automake nettle-dev
 
     - name: "Install gtar wrapper"
       if: ${{ startsWith(matrix.os, 'macos') }}

.gitignore

@@ -25,6 +25,7 @@ aminclude_static.am
 src/include/config.h
 src/include/config.h.in
 src/include/config.h.in~
+/config.cache
 /config.log
 /config.status
 /configure

CLAUDE.md

@@ -0,0 +1,86 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## What is Mosh
+
+Mosh (mobile shell) is a remote terminal application that supports intermittent connectivity and roaming. Unlike SSH, it uses UDP and synchronizes terminal state as diffs, allowing the client to do predictive local echo and survive network changes.
+
+## Build System
+
+Mosh uses GNU Autotools (Autoconf/Automake).
+
+```bash
+./autogen.sh          # Generate build scripts (required after cloning)
+./configure           # Configure build
+make                  # Build
+make check            # Run all tests
+```
+
+Useful configure options:
+- `--enable-compile-warnings=error` — treat warnings as errors
+- `--enable-asan` — enable AddressSanitizer
+- `--enable-code-coverage` — enable coverage reporting
+- `--with-crypto-library=openssl|nettle|apple-common-crypto` — choose crypto backend (default: autodetect)
+- `--disable-client` / `--disable-server` — build only one side
+
+## Running Tests
+
+```bash
+make check              # Run all tests
+make V=1 check          # Verbose output
+make check-code-coverage  # Coverage report (requires --enable-code-coverage)
+```
+
+Test types:
+- **Unit tests** (`src/tests/`): ocb-aes, encrypt-decrypt, base64, nonce-incr, is-utf8-locale
+- **End-to-end tests**: tmux-based display/network/unicode/resize tests (see `src/tests/README.md`)
+
+## Static Analysis / Linting
+
+```bash
+make cppcheck    # cppcheck static analysis
+make scan-build  # Clang static analyzer
+```
+
+Code style uses `.clang-format` (Mozilla-based, 116-column limit). CI enforces clang-format on PRs.
+
+## Dependencies
+
+Ubuntu/Debian:
+```bash
+sudo apt install build-essential protobuf-compiler libprotobuf-dev pkg-config \
+    libutempter-dev zlib1g-dev libncurses5-dev libssl-dev bash-completion tmux less
+```
+
+## Architecture
+
+```
+src/
+  frontend/    — mosh-client.cc, mosh-server.cc entry points
+  crypto/      — AES-OCB encryption; supports OpenSSL, Nettle, Apple Common Crypto
+  network/     — UDP transport, state sync, compression, fragmentation
+  terminal/    — Terminal emulator, Unicode, character cell rendering
+  statesync/   — State diff/sync logic between client and server
+  protobufs/   — Protobuf definitions (hostinput, userinput, transportinstruction)
+  util/        — PTY, locale, timestamps, select wrapper
+  tests/       — Unit + end-to-end tests
+  fuzz/        — Fuzzing targets
+```
+
+**Data flow:**
+1. `mosh-client` SSHes to server, spawns `mosh-server`
+2. Server sends AES-128 key + UDP port over SSH, then SSH closes
+3. Client and server exchange terminal state diffs over UDP
+4. Client applies predictive local echo using its own terminal emulator
+5. Server sends authoritative state; client reconciles
+
+**Crypto:** AES-128-OCB with a fresh key per session. Key is passed out-of-band via SSH. The crypto backend is selected at configure time; the abstraction lives in `src/crypto/`.
+
+**State sync:** Both ends maintain a `Terminal::Complete` object. The network layer (`src/network/`) sends `TransportInstruction` protobufs containing diffs. The client uses `src/statesync/` to apply them.
+
+## Security Notes (from README)
+
+- Hardening flags enabled by default (`-fstack-protector-all`, `-D_FORTIFY_SOURCE=2`, `-fPIE`, RELRO, etc.)
+- `mosh-server` must ensure process environment is not readable by other users before writing the session key to stdout
+- C++17 is required minimum (protobuf compatibility)

configure.ac

@@ -40,7 +40,7 @@ AC_ARG_ENABLE([compile-warnings],
        ;;
      maximum)
        WARNING_CXXFLAGS="-Wall"
-       PICKY_CXXFLAGS="-Wextra -pedantic -Wno-long-long -Weffc++ -Wmissing-declarations"
+       PICKY_CXXFLAGS="-Wextra -Wno-long-long -Weffc++ -Wmissing-declarations"
        ;;
      error)
        # remove -Wno-c++17-extensions once protocolbuffers/protobuf#9181 is
@@ -48,11 +48,11 @@ AC_ARG_ENABLE([compile-warnings],
        # remove -Wno-unused-parameter once
        # protocolbuffers/protobuf#10357 is resolved       
        WARNING_CXXFLAGS="-Wall -Werror -Wno-c++17-extensions"
-       PICKY_CXXFLAGS="-Wextra -pedantic -Wno-long-long -Weffc++ -Wmissing-declarations -Wno-unused-parameter"
+       PICKY_CXXFLAGS="-Wextra -Wno-long-long -Weffc++ -Wmissing-declarations -Wno-unused-parameter"
        ;;
      distcheck)
        WARNING_CXXFLAGS="-Wall -Werror"
-       PICKY_CXXFLAGS="-Wextra -pedantic -Wno-long-long -Weffc++ -Wmissing-declarations"
+       PICKY_CXXFLAGS="-Wextra -Wno-long-long -Weffc++ -Wmissing-declarations"
        AX_CHECK_COMPILE_FLAG([-Wno-error=unused-parameter],
          [PICKY_CXXFLAGS="$PICKY_CXXFLAGS -Wno-error=unused-parameter"], [], [-Werror])
        AX_CHECK_COMPILE_FLAG([-Wno-error=c++11-extensions],
@@ -272,6 +272,7 @@ AC_CHECK_HEADERS(m4_normalize([
   stdlib.h
   string.h
   sys/ioctl.h
+  sys/random.h
   sys/resource.h
   sys/socket.h
   sys/stat.h
@@ -304,6 +305,8 @@ AC_TYPE_UINTPTR_T
 
 # Checks for library functions.
 AC_CHECK_FUNCS(m4_normalize([
+  getentropy
+  getrandom
   gettimeofday
   posix_memalign
   cfmakeraw

debian/changelog

@@ -1,3 +1,9 @@
+mosh (1.4.0-2) UNRELEASED; urgency=medium
+
+  * Remove Benjamin Barenblat from Uploaders.
+
+ -- Benjamin Barenblat <bbaren@debian.org>  Mon, 19 Jan 2026 19:38:42 -0500
+
 mosh (1.4.0-1) unstable; urgency=medium
 
   * New upstream release.

debian/control

@@ -2,7 +2,7 @@ Source: mosh
 Section: net
 Priority: optional
 Maintainer: Keith Winstein <keithw@mit.edu>
-Uploaders: Alex Chernyakhovsky <achernya@debian.org>, Benjamin Barenblat <bbaren@debian.org>
+Uploaders: Alex Chernyakhovsky <achernya@debian.org>
 Build-Depends: debhelper-compat (= 12), protobuf-compiler, libprotobuf-dev, pkg-config, libutempter-dev, zlib1g-dev, libncurses5-dev, libssl-dev, bash-completion, locales <!nocheck>, tmux <!nocheck>, less <!nocheck>
 Rules-Requires-Root: binary-targets
 Standards-Version: 4.6.1

src/crypto/prng.h

@@ -33,6 +33,20 @@
 #ifndef PRNG_HPP
 #define PRNG_HPP
 
+#include "config.h"
+
+#if !defined( HAVE_GETENTROPY ) && !defined( HAVE_GETRANDOM )
+#define HAVE_URANDOM 1
+#else
+#undef HAVE_URANDOM
+#endif
+
+#include <unistd.h>
+#ifdef HAVE_SYS_RANDOM_H
+#include <sys/random.h>
+#endif
+
+#include <algorithm>
 #include <cstdint>
 #include <fstream>
 #include <string>
@@ -43,21 +57,29 @@
 
    We rely on stdio buffering for efficiency. */
 
+#ifdef HAVE_URANDOM
 static const char rdev[] = "/dev/urandom";
+#endif
 
 using namespace Crypto;
 
 class PRNG
 {
 private:
+#ifdef HAVE_URANDOM
   std::ifstream randfile;
+#endif
 
   /* unimplemented to satisfy -Weffc++ */
   PRNG( const PRNG& );
   PRNG& operator=( const PRNG& );
 
 public:
-  PRNG() : randfile( rdev, std::ifstream::in | std::ifstream::binary ) {}
+  PRNG()
+#ifdef HAVE_URANDOM
+    : randfile( rdev, std::ifstream::in | std::ifstream::binary )
+#endif
+  {}
 
   void fill( void* dest, size_t size )
   {
@@ -65,10 +87,27 @@ public:
       return;
     }
 
+#if defined( HAVE_GETRANDOM )
+    if ( getrandom( dest, size, 0 ) != static_cast<ssize_t>( size ) ) {
+      throw CryptoException( "getrandom fell short" );
+    }
+#elif defined( HAVE_GETENTROPY )
+    // getentropy() can only read up to 256 bytes at a time :(.
+    const size_t max_read = 256;
+    while ( size ) {
+      size_t this_size = std::min( max_read, size );
+      if ( getentropy( dest, this_size ) ) {
+        throw CryptoException( "getentropy fell short" );
+      }
+      size -= this_size;
+      dest = static_cast<char*>( dest ) + this_size;
+    }
+#else
     randfile.read( static_cast<char*>( dest ), size );
     if ( !randfile ) {
       throw CryptoException( "Could not read from " + std::string( rdev ) );
     }
+#endif
   }
 
   uint8_t uint8()

src/frontend/mosh-client.cc

@@ -105,11 +105,7 @@ static void print_colorcount( void )
   printf( "%d\n", color_val );
 }
 
-#ifdef NACL
-int mosh_main( int argc, char* argv[] )
-#else
 int main( int argc, char* argv[] )
-#endif
 {
   unsigned int verbose = 0;
   /* For security, make sure we don't dump core */

src/terminal/terminalframebuffer.h

@@ -427,8 +427,9 @@ public:
     if ( row == -1 )
       row = ds.get_cursor_row();
     row_pointer& mutable_row = rows.at( row );
-    // If the row is shared, copy it.
-    if ( !mutable_row.unique() ) {
+    // If the row is shared, copy it. This is only safe because mosh isn't
+    // multi-threaded.
+    if ( mutable_row.use_count() > 1 ) {
       mutable_row = std::make_shared<Row>( *mutable_row );
     }
     return mutable_row.get();

src/util/select.h

@@ -108,7 +108,7 @@ public:
     /* Register a handler, which will only be called when pselect()
        is interrupted by a (possibly queued) signal. */
     struct sigaction sa;
-    sa.sa_flags = 0;
+    sa.sa_flags = SA_RESTART;
     sa.sa_handler = &handle_signal;
     fatal_assert( 0 == sigfillset( &sa.sa_mask ) );
     fatal_assert( 0 == sigaction( signum, &sa, NULL ) );