util: Add RAII TokenPipe

1 files changed, 127 insertions, 0 deletions

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