util: Add RAII TokenPipe

3 files changed, 237 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 8a9ef49a34..6a7a49f012 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -249,6 +249,7 @@ BITCOIN_CORE_H = \
   util/system.h \
   util/threadnames.h \
   util/time.h \
+  util/tokenpipe.h \
   util/trace.h \
   util/translation.h \
   util/ui_change_type.h \
@@ -577,6 +578,7 @@ libbitcoin_util_a_SOURCES = \
   util/strencodings.cpp \
   util/string.cpp \
   util/time.cpp \
+  util/tokenpipe.cpp \
   $(BITCOIN_CORE_H)
 
 if USE_LIBEVENT
diff --git a/src/util/tokenpipe.cpp b/src/util/tokenpipe.cpp
new file mode 100644
index 0000000000..79465dd430
--- /dev/null
+++ b/src/util/tokenpipe.cpp
@@ -0,0 +1,108 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#include <util/tokenpipe.h>
+
+#include <config/bitcoin-config.h>
+
+#ifndef WIN32
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+TokenPipeEnd TokenPipe::TakeReadEnd()
+{
+    TokenPipeEnd res(m_fds[0]);
+    m_fds[0] = -1;
+    return res;
+}
+
+TokenPipeEnd TokenPipe::TakeWriteEnd()
+{
+    TokenPipeEnd res(m_fds[1]);
+    m_fds[1] = -1;
+    return res;
+}
+
+TokenPipeEnd::TokenPipeEnd(int fd) : m_fd(fd)
+{
+}
+
+TokenPipeEnd::~TokenPipeEnd()
+{
+    Close();
+}
+
+int TokenPipeEnd::TokenWrite(uint8_t token)
+{
+    while (true) {
+        ssize_t result = write(m_fd, &token, 1);
+        if (result < 0) {
+            // Failure. It's possible that the write was interrupted by a signal,
+            // in that case retry.
+            if (errno != EINTR) {
+                return TS_ERR;
+            }
+        } else if (result == 0) {
+            return TS_EOS;
+        } else { // ==1
+            return 0;
+        }
+    }
+}
+
+int TokenPipeEnd::TokenRead()
+{
+    uint8_t token;
+    while (true) {
+        ssize_t result = read(m_fd, &token, 1);
+        if (result < 0) {
+            // Failure. Check if the read was interrupted by a signal,
+            // in that case retry.
+            if (errno != EINTR) {
+                return TS_ERR;
+            }
+        } else if (result == 0) {
+            return TS_EOS;
+        } else { // ==1
+            return token;
+        }
+    }
+    return token;
+}
+
+void TokenPipeEnd::Close()
+{
+    if (m_fd != -1) close(m_fd);
+    m_fd = -1;
+}
+
+std::optional<TokenPipe> TokenPipe::Make()
+{
+    int fds[2] = {-1, -1};
+#if HAVE_O_CLOEXEC && HAVE_DECL_PIPE2
+    if (pipe2(fds, O_CLOEXEC) != 0) {
+        return std::nullopt;
+    }
+#else
+    if (pipe(fds) != 0) {
+        return std::nullopt;
+    }
+#endif
+    return TokenPipe(fds);
+}
+
+TokenPipe::~TokenPipe()
+{
+    Close();
+}
+
+void TokenPipe::Close()
+{
+    if (m_fds[0] != -1) close(m_fds[0]);
+    if (m_fds[1] != -1) close(m_fds[1]);
+    m_fds[0] = m_fds[1] = -1;
+}
+
+#endif // WIN32
diff --git a/src/util/tokenpipe.h b/src/util/tokenpipe.h
new file mode 100644
index 0000000000..f56be93a38
--- /dev/null
+++ b/src/util/tokenpipe.h
@@ -0,0 +1,127 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_TOKENPIPE_H
+#define BITCOIN_UTIL_TOKENPIPE_H
+
+#ifndef WIN32
+
+#include <cstdint>
+#include <optional>
+
+/** One end of a token pipe. */
+class TokenPipeEnd
+{
+private:
+    int m_fd = -1;
+
+public:
+    TokenPipeEnd(int fd = -1);
+    ~TokenPipeEnd();
+
+    /** Return value constants for TokenWrite and TokenRead. */
+    enum Status {
+        TS_ERR = -1, //!< I/O error
+        TS_EOS = -2, //!< Unexpected end of stream
+    };
+
+    /** Write token to endpoint.
+     *
+     * @returns 0       If successful.
+     *          <0 if error:
+     *            TS_ERR  If an error happened.
+     *            TS_EOS  If end of stream happened.
+     */
+    int TokenWrite(uint8_t token);
+
+    /** Read token from endpoint.
+     *
+     * @returns >=0     Token value, if successful.
+     *          <0 if error:
+     *            TS_ERR  If an error happened.
+     *            TS_EOS  If end of stream happened.
+     */
+    int TokenRead();
+
+    /** Explicit close function.
+     */
+    void Close();
+
+    /** Return whether endpoint is open.
+     */
+    bool IsOpen() { return m_fd != -1; }
+
+    // Move-only class.
+    TokenPipeEnd(TokenPipeEnd&& other)
+    {
+        m_fd = other.m_fd;
+        other.m_fd = -1;
+    }
+    TokenPipeEnd& operator=(TokenPipeEnd&& other)
+    {
+        Close();
+        m_fd = other.m_fd;
+        other.m_fd = -1;
+        return *this;
+    }
+    TokenPipeEnd(const TokenPipeEnd&) = delete;
+    TokenPipeEnd& operator=(const TokenPipeEnd&) = delete;
+};
+
+/** An interprocess or interthread pipe for sending tokens (one-byte values)
+ * over.
+ */
+class TokenPipe
+{
+private:
+    int m_fds[2] = {-1, -1};
+
+    TokenPipe(int fds[2]) : m_fds{fds[0], fds[1]} {}
+
+public:
+    ~TokenPipe();
+
+    /** Create a new pipe.
+     * @returns The created TokenPipe, or an empty std::nullopt in case of error.
+     */
+    static std::optional<TokenPipe> Make();
+
+    /** Take the read end of this pipe. This can only be called once,
+     * as the object will be moved out.
+     */
+    TokenPipeEnd TakeReadEnd();
+
+    /** Take the write end of this pipe. This should only be called once,
+     * as the object will be moved out.
+     */
+    TokenPipeEnd TakeWriteEnd();
+
+    /** Close and end of the pipe that hasn't been moved out.
+     */
+    void Close();
+
+    // Move-only class.
+    TokenPipe(TokenPipe&& other)
+    {
+        for (int i = 0; i < 2; ++i) {
+            m_fds[i] = other.m_fds[i];
+            other.m_fds[i] = -1;
+        }
+    }
+    TokenPipe& operator=(TokenPipe&& other)
+    {
+        Close();
+        for (int i = 0; i < 2; ++i) {
+            m_fds[i] = other.m_fds[i];
+            other.m_fds[i] = -1;
+        }
+        return *this;
+    }
+    TokenPipe(const TokenPipe&) = delete;
+    TokenPipe& operator=(const TokenPipe&) = delete;
+};
+
+#endif // WIN32
+
+#endif // BITCOIN_UTIL_TOKENPIPE_H