Add C API to QPDFLogger

23 files changed, 592 insertions, 15 deletions

diff --git a/ChangeLog b/ChangeLog
index 97e8506c..abf10459 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2022-06-18  Jay Berkenbilt  <ejb@ql.org>
 
+        * Add examples that show how to capture QPDFJob's output by
+        configuring the default logger (qpdfjob-save-attachment.cc,
+        qpdfjob-c-save-attachment.c). Fixes #691.
+
+        * Add C API for QPDFLogger -- see qpdflogger-c.h
+
         * Add additional qpdfjob C API functions take a handle.
 
         * Add qpdf_exit_code_e to Constants.h so that exit codes from
diff --git a/include/qpdf/QPDFLogger.hh b/include/qpdf/QPDFLogger.hh
index cd439caa..54ab7efe 100644
--- a/include/qpdf/QPDFLogger.hh
+++ b/include/qpdf/QPDFLogger.hh
@@ -130,9 +130,9 @@ class QPDFLogger
     void setError(std::shared_ptr<Pipeline>);
     // See notes above about the save pipeline
     QPDF_DLL
-    void setSave(std::shared_ptr<Pipeline>);
+    void setSave(std::shared_ptr<Pipeline>, bool only_if_not_set);
     QPDF_DLL
-    void saveToStandardOutput();
+    void saveToStandardOutput(bool only_if_not_set);
 
     // Shortcut for logic to reset output to new output/error streams.
     // out_stream is used for info, err_stream is used for error, and
diff --git a/include/qpdf/qpdflogger-c.h b/include/qpdf/qpdflogger-c.h
new file mode 100644
index 00000000..9d31f79c
--- /dev/null
+++ b/include/qpdf/qpdflogger-c.h
@@ -0,0 +1,100 @@
+/* Copyright (c) 2005-2022 Jay Berkenbilt
+ *
+ * This file is part of qpdf.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Versions of qpdf prior to version 7 were released under the terms
+ * of version 2.0 of the Artistic License. At your option, you may
+ * continue to consider qpdf to be licensed under those terms. Please
+ * see the manual for additional information.
+ */
+
+#ifndef QPDFLOGGER_H
+#define QPDFLOGGER_H
+
+/*
+ * This file provides a C API for QPDFLogger. See QPDFLogger.hh for
+ * information about the logger.
+ */
+
+#include <qpdf/DLL.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+    /* To operate on a logger, you need a handle to it. call
+     * qpdflogger_default_logger to get a handle for the default
+     * logger. The qpdf and qpdfjob functions may offer ways to get
+     * other logger handles. When you're done with the logger handler,
+     * call qpdflogger_cleanup. This does not destroy the underlying
+     * log object. It just cleans up the handle to it.
+     */
+
+    typedef struct _qpdflogger_handle* qpdflogger_handle;
+    QPDF_DLL
+    qpdflogger_handle qpdflogger_default_logger();
+
+    QPDF_DLL
+    void qpdflogger_cleanup(qpdflogger_handle* l);
+
+    enum qpdf_log_dest_e {
+        qpdf_log_dest_default = 0,
+        qpdf_log_dest_stdout = 1,
+        qpdf_log_dest_stderr = 2,
+        qpdf_log_dest_discard = 3,
+        qpdf_log_dest_custom = 4,
+    };
+
+    typedef void (*qpdf_log_fn_t)(char const* data, size_t len, void* udata);
+
+    QPDF_DLL
+    void qpdflogger_set_info(
+        qpdflogger_handle l,
+        enum qpdf_log_dest_e dest,
+        qpdf_log_fn_t fn,
+        void* udata);
+    QPDF_DLL
+    void qpdflogger_set_warn(
+        qpdflogger_handle l,
+        enum qpdf_log_dest_e dest,
+        qpdf_log_fn_t fn,
+        void* udata);
+    QPDF_DLL
+    void qpdflogger_set_error(
+        qpdflogger_handle l,
+        enum qpdf_log_dest_e dest,
+        qpdf_log_fn_t fn,
+        void* udata);
+
+    /* A non-zero value for only_if_not_set means that the save
+     * pipeline will only be changed if it is not already set.
+     */
+    QPDF_DLL
+    void qpdflogger_set_save(
+        qpdflogger_handle l,
+        enum qpdf_log_dest_e dest,
+        qpdf_log_fn_t fn,
+        void* udata,
+        int only_if_not_set);
+    QPDF_DLL
+    void qpdflogger_save_to_standard_output(
+        qpdflogger_handle l, int only_if_not_set);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // QPDFLOGGER_H
diff --git a/libqpdf/CMakeLists.txt b/libqpdf/CMakeLists.txt
index a6b036a7..3c14115b 100644
--- a/libqpdf/CMakeLists.txt
+++ b/libqpdf/CMakeLists.txt
@@ -110,7 +110,8 @@ set(libqpdf_SOURCES
   SF_FlateLzwDecode.cc
   SparseOHArray.cc
   qpdf-c.cc
-  qpdfjob-c.cc)
+  qpdfjob-c.cc
+  qpdflogger-c.cc)
 
 include(FindPkgConfig)
 include(CheckTypeSize)
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index b25257a1..606a612a 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -710,7 +710,7 @@ QPDFJob::checkConfiguration()
         save_to_stdout = true;
     }
     if (save_to_stdout) {
-        this->m->log->saveToStandardOutput();
+        this->m->log->saveToStandardOutput(true);
     }
     if ((!m->split_pages) &&
         QUtil::same_file(m->infilename.get(), m->outfilename.get())) {
@@ -925,7 +925,7 @@ QPDFJob::doShowObj(QPDF& pdf)
             } else {
                 // If anything has been written to standard output,
                 // this will fail.
-                this->m->log->saveToStandardOutput();
+                this->m->log->saveToStandardOutput(true);
                 obj.pipeStreamData(
                     this->m->log->getSave().get(),
                     (filter && m->normalize) ? qpdf_ef_normalize : 0,
@@ -1031,7 +1031,7 @@ QPDFJob::doShowAttachment(QPDF& pdf)
     auto efs = fs->getEmbeddedFileStream();
     // saveToStandardOutput has already been called, but it's harmless
     // to call it again, so do as defensive coding.
-    this->m->log->saveToStandardOutput();
+    this->m->log->saveToStandardOutput(true);
     efs.pipeStreamData(this->m->log->getSave().get(), 0, qpdf_dl_all);
 }
 
@@ -3289,7 +3289,7 @@ QPDFJob::writeOutfile(QPDF& pdf)
         } else {
             // saveToStandardOutput has already been called, but
             // calling it again is defensive and harmless.
-            this->m->log->saveToStandardOutput();
+            this->m->log->saveToStandardOutput(true);
             w.setOutputPipeline(this->m->log->getSave().get());
         }
         setWriterOptions(pdf, w);
diff --git a/libqpdf/QPDFLogger.cc b/libqpdf/QPDFLogger.cc
index 3b25c050..78cb2a32 100644
--- a/libqpdf/QPDFLogger.cc
+++ b/libqpdf/QPDFLogger.cc
@@ -181,8 +181,11 @@ QPDFLogger::setError(std::shared_ptr<Pipeline> p)
 }
 
 void
-QPDFLogger::setSave(std::shared_ptr<Pipeline> p)
+QPDFLogger::setSave(std::shared_ptr<Pipeline> p, bool only_if_not_set)
 {
+    if (only_if_not_set && (this->m->p_save != nullptr)) {
+        return;
+    }
     if (this->m->p_save == p) {
         return;
     }
@@ -202,9 +205,9 @@ QPDFLogger::setSave(std::shared_ptr<Pipeline> p)
 }
 
 void
-QPDFLogger::saveToStandardOutput()
+QPDFLogger::saveToStandardOutput(bool only_if_not_set)
 {
-    setSave(standardOutput());
+    setSave(standardOutput(), only_if_not_set);
 }
 
 void
diff --git a/libqpdf/qpdflogger-c.cc b/libqpdf/qpdflogger-c.cc
new file mode 100644
index 00000000..46fd9fba
--- /dev/null
+++ b/libqpdf/qpdflogger-c.cc
@@ -0,0 +1,163 @@
+#include <qpdf/qpdflogger-c.h>
+
+#include <qpdf/Pipeline.hh>
+#include <qpdf/QIntC.hh>
+#include <qpdf/QPDFLogger.hh>
+#include <functional>
+#include <memory>
+
+struct _qpdflogger_handle
+{
+    _qpdflogger_handle(std::shared_ptr<QPDFLogger> l);
+    ~_qpdflogger_handle() = default;
+
+    std::shared_ptr<QPDFLogger> l;
+};
+
+namespace
+{
+    class FunctionPipeline: public Pipeline
+    {
+      public:
+        FunctionPipeline(char const* identifier, qpdf_log_fn_t fn, void* udata);
+        virtual ~FunctionPipeline() = default;
+
+        virtual void write(unsigned char const* buf, size_t len) override;
+        virtual void finish() override;
+
+      private:
+        qpdf_log_fn_t fn;
+        void* udata;
+    };
+}; // namespace
+
+FunctionPipeline::FunctionPipeline(
+    char const* identifier, qpdf_log_fn_t fn, void* udata) :
+    Pipeline(identifier, nullptr),
+    fn(fn),
+    udata(udata)
+{
+}
+
+void
+FunctionPipeline::write(unsigned char const* buf, size_t len)
+{
+    fn(reinterpret_cast<char const*>(buf), QIntC::to_ulong(len), udata);
+}
+
+void
+FunctionPipeline::finish()
+{
+    // Nothing needed
+}
+
+_qpdflogger_handle::_qpdflogger_handle(std::shared_ptr<QPDFLogger> l) :
+    l(l)
+{
+}
+
+qpdflogger_handle
+qpdflogger_default_logger()
+{
+    return new _qpdflogger_handle(QPDFLogger::defaultLogger());
+}
+
+void
+qpdflogger_cleanup(qpdflogger_handle* l)
+{
+    delete *l;
+    *l = nullptr;
+}
+
+static void
+set_log_dest(
+    QPDFLogger* l,
+    std::function<void(std::shared_ptr<Pipeline>)> method,
+    qpdf_log_dest_e dest,
+    char const* identifier,
+    qpdf_log_fn_t fn,
+    void* udata)
+{
+    switch (dest) {
+    case qpdf_log_dest_default:
+        method(nullptr);
+        break;
+    case qpdf_log_dest_stdout:
+        method(l->standardOutput());
+        break;
+    case qpdf_log_dest_stderr:
+        method(l->standardError());
+        break;
+    case qpdf_log_dest_discard:
+        method(l->discard());
+        break;
+    case qpdf_log_dest_custom:
+        method(std::make_shared<FunctionPipeline>(identifier, fn, udata));
+        break;
+    }
+}
+
+static void
+set_log_dest(
+    QPDFLogger* l,
+    void (QPDFLogger::*method)(std::shared_ptr<Pipeline>),
+    qpdf_log_dest_e dest,
+    char const* identifier,
+    qpdf_log_fn_t fn,
+    void* udata)
+{
+    set_log_dest(
+        l,
+        std::bind(std::mem_fn(method), l, std::placeholders::_1),
+        dest,
+        identifier,
+        fn,
+        udata);
+}
+
+void
+qpdflogger_set_info(
+    qpdflogger_handle l, qpdf_log_dest_e dest, qpdf_log_fn_t fn, void* udata)
+{
+    set_log_dest(
+        l->l.get(), &QPDFLogger::setInfo, dest, "info logger", fn, udata);
+}
+
+void
+qpdflogger_set_warn(
+    qpdflogger_handle l, qpdf_log_dest_e dest, qpdf_log_fn_t fn, void* udata)
+{
+    set_log_dest(
+        l->l.get(), &QPDFLogger::setWarn, dest, "warn logger", fn, udata);
+}
+
+void
+qpdflogger_set_error(
+    qpdflogger_handle l, qpdf_log_dest_e dest, qpdf_log_fn_t fn, void* udata)
+{
+    set_log_dest(
+        l->l.get(), &QPDFLogger::setError, dest, "error logger", fn, udata);
+}
+
+void
+qpdflogger_set_save(
+    qpdflogger_handle l,
+    qpdf_log_dest_e dest,
+    qpdf_log_fn_t fn,
+    void* udata,
+    int only_if_not_set)
+{
+    auto method = std::bind(
+        std::mem_fn(&QPDFLogger::setSave),
+        l->l.get(),
+        std::placeholders::_1,
+        only_if_not_set);
+    set_log_dest(l->l.get(), method, dest, "save logger", fn, udata);
+}
+
+void
+qpdflogger_save_to_standard_output(qpdflogger_handle l, int only_if_not_set)
+{
+    qpdflogger_set_save(
+        l, qpdf_log_dest_stdout, nullptr, nullptr, only_if_not_set);
+}
diff --git a/libtests/CMakeLists.txt b/libtests/CMakeLists.txt
index 196cd3eb..62ba390e 100644
--- a/libtests/CMakeLists.txt
+++ b/libtests/CMakeLists.txt
@@ -33,10 +33,18 @@ set(TEST_PROGRAMS
   runlength
   sha2
   sparse_array)
+set(TEST_C_PROGRAMS
+  logger_c)
+
 foreach(PROG ${TEST_PROGRAMS})
   add_executable(${PROG} ${PROG}.cc)
   target_link_libraries(${PROG} libqpdf_object)
 endforeach()
+foreach(PROG ${TEST_C_PROGRAMS})
+  add_executable(${PROG} ${PROG}.c)
+  target_link_libraries(${PROG} libqpdf_object)
+  set_property(TARGET ${PROG} PROPERTY LINKER_LANGUAGE CXX)
+endforeach()
 
 # Since libtests link with the object library and don't use the DLL,
 # we don't need to (and shouldn't) add the libqpdf target directory to
diff --git a/libtests/logger.cc b/libtests/logger.cc
index f10319f6..b968422e 100644
--- a/libtests/logger.cc
+++ b/libtests/logger.cc
@@ -22,7 +22,7 @@ test1()
         *(logger->getInfo()) << "getSave exception: " << e.what() << "\n";
     }
     try {
-        logger->saveToStandardOutput();
+        logger->saveToStandardOutput(true);
         assert(false);
     } catch (std::logic_error& e) {
         *(logger->getInfo())
@@ -40,12 +40,12 @@ test2()
     // First call saveToStandardOutput. Then use info, which then to
     // go stderr.
     QPDFLogger l;
-    l.saveToStandardOutput();
+    l.saveToStandardOutput(true);
     l.info(std::string("info to stderr\n"));
     *(l.getSave()) << "save to stdout\n";
     l.setInfo(nullptr);
     l.info("info still to stderr\n");
-    l.setSave(nullptr);
+    l.setSave(nullptr, false);
     l.setInfo(nullptr);
     l.info("info back to stdout\n");
 }
diff --git a/libtests/logger_c.c b/libtests/logger_c.c
new file mode 100644
index 00000000..94815601
--- /dev/null
+++ b/libtests/logger_c.c
@@ -0,0 +1,108 @@
+#include <qpdf/assert_test.h>
+
+#include <qpdf/qpdflogger-c.h>
+
+#include <qpdf/Constants.h>
+#include <qpdf/qpdfjob-c.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+static void
+fn(char const* data, size_t len, void* udata)
+{
+    FILE* f = (FILE*)udata;
+    fwrite(data, 1, len, f);
+}
+
+static void
+do_run(char const* json, int exp_status)
+{
+    int status = qpdfjob_run_from_json(json);
+    assert(status == exp_status);
+}
+
+static FILE*
+do_fopen(char const* filename)
+{
+    FILE* f = NULL;
+#ifdef _MSC_VER
+    if (fopen_s(&f, filename, "wb") != 0) {
+        f = NULL;
+    }
+#else
+    f = fopen(filename, "wb");
+#endif
+    if (f == NULL) {
+        fprintf(stderr, "unable to open %s\n", filename);
+        exit(2);
+    }
+    return f;
+}
+
+int
+main()
+{
+    FILE* info = do_fopen("info");
+    FILE* warn = do_fopen("warn");
+    FILE* error = do_fopen("error");
+    FILE* save = do_fopen("save");
+    FILE* save2 = do_fopen("save2");
+    qpdflogger_handle l = qpdflogger_default_logger();
+
+    qpdflogger_set_info(l, qpdf_log_dest_custom, fn, (void*)info);
+    qpdflogger_set_warn(l, qpdf_log_dest_custom, fn, (void*)warn);
+    qpdflogger_set_error(l, qpdf_log_dest_custom, fn, (void*)error);
+    qpdflogger_set_save(l, qpdf_log_dest_custom, fn, (void*)save, 0);
+
+    do_run(
+        "{\"inputFile\": \"normal.pdf\", \"showNpages\": \"\"}",
+        qpdf_exit_success);
+    do_run(
+        "{\"inputFile\": \"warning.pdf\", \"showNpages\": \"\"}",
+        qpdf_exit_warning);
+    do_run(
+        "{\"inputFile\": \"missing.pdf\", \"showNpages\": \"\"}",
+        qpdf_exit_error);
+    do_run(
+        "{\"inputFile\": \"normal.pdf\","
+        " \"staticId\": \"\","
+        " \"outputFile\": \"-\"}",
+        qpdf_exit_success);
+
+    fclose(info);
+    fclose(warn);
+    fclose(error);
+    fclose(save);
+
+    qpdflogger_set_info(l, qpdf_log_dest_stderr, NULL, NULL);
+    qpdflogger_set_warn(l, qpdf_log_dest_stdout, NULL, NULL);
+    qpdflogger_set_error(l, qpdf_log_dest_default, NULL, NULL);
+    qpdflogger_set_save(l, qpdf_log_dest_custom, fn, (void*)save2, 0);
+
+    do_run(
+        "{\"inputFile\": \"2pages.pdf\", \"showNpages\": \"\"}",
+        qpdf_exit_success);
+    do_run(
+        "{\"inputFile\": \"warning.pdf\", \"showNpages\": \"\"}",
+        qpdf_exit_warning);
+    do_run(
+
+        "{\"inputFile\": \"missing.pdf\", \"showNpages\": \"\"}",
+        qpdf_exit_error);
+    do_run(
+        "{\"inputFile\": \"attach.pdf\","
+        " \"showAttachment\": \"a\"}",
+        qpdf_exit_success);
+
+    /* This won't change save since it's already set */
+    qpdflogger_save_to_standard_output(l, 1);
+    do_run(
+        "{\"inputFile\": \"attach.pdf\","
+        " \"showAttachment\": \"a\"}",
+        qpdf_exit_success);
+
+    qpdflogger_cleanup(&l);
+
+    return 0;
+}
diff --git a/libtests/qtest/logger.test b/libtests/qtest/logger.test
index 86767eff..786af4fb 100644
--- a/libtests/qtest/logger.test
+++ b/libtests/qtest/logger.test
@@ -24,10 +24,22 @@ $td->runtest("check stderr",
              {$td->FILE => "exp-stderr"},
              $td->NORMALIZE_NEWLINES);
 
+$td->runtest("logger C API",
+             {$td->COMMAND => "logger_c >stdout 2>stderr"},
+             {$td->STRING => "", $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
+foreach my $f (qw(stdout stderr info warn error save save2))
+{
+    $td->runtest("check $f (C)",
+                 {$td->FILE => "$f"},
+                 {$td->FILE => "c-exp-$f"},
+                 $td->NORMALIZE_NEWLINES);
+}
+
 cleanup();
-$td->report(3);
+$td->report(11);
 
 sub cleanup
 {
-    unlink "stdout", "stderr";
+    unlink "stdout", "stderr", "info", "warn", "error", "save", "save2";
 }
diff --git a/libtests/qtest/logger/2pages.pdf b/libtests/qtest/logger/2pages.pdf
new file mode 100644
index 00000000..f3e1700d
--- /dev/null
+++ b/libtests/qtest/logger/2pages.pdf
diff --git a/libtests/qtest/logger/attach.pdf b/libtests/qtest/logger/attach.pdf
new file mode 100644
index 00000000..bbc09588
--- /dev/null
+++ b/libtests/qtest/logger/attach.pdf
diff --git a/libtests/qtest/logger/c-exp-error b/libtests/qtest/logger/c-exp-error
new file mode 100644
index 00000000..8e33a38a
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-error
@@ -0,0 +1 @@
+qpdfjob json: open missing.pdf: No such file or directory
diff --git a/libtests/qtest/logger/c-exp-info b/libtests/qtest/logger/c-exp-info
new file mode 100644
index 00000000..6ed281c7
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-info
@@ -0,0 +1,2 @@
+1
+1
diff --git a/libtests/qtest/logger/c-exp-save b/libtests/qtest/logger/c-exp-save
new file mode 100644
index 00000000..b8c692ed
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-save
diff --git a/libtests/qtest/logger/c-exp-save2 b/libtests/qtest/logger/c-exp-save2
new file mode 100644
index 00000000..3d1fe696
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-save2
@@ -0,0 +1,2 @@
+quack
+quack
diff --git a/libtests/qtest/logger/c-exp-stderr b/libtests/qtest/logger/c-exp-stderr
new file mode 100644
index 00000000..bfbb2cff
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-stderr
@@ -0,0 +1,3 @@
+2
+1
+qpdfjob json: open missing.pdf: No such file or directory
diff --git a/libtests/qtest/logger/c-exp-stdout b/libtests/qtest/logger/c-exp-stdout
new file mode 100644
index 00000000..e7566de7
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-stdout
@@ -0,0 +1,4 @@
+WARNING: warning.pdf: file is damaged
+WARNING: warning.pdf (offset 1556): xref not found
+WARNING: warning.pdf: Attempting to reconstruct cross-reference table
+qpdfjob json: operation succeeded with warnings
diff --git a/libtests/qtest/logger/c-exp-warn b/libtests/qtest/logger/c-exp-warn
new file mode 100644
index 00000000..e7566de7
--- /dev/null
+++ b/libtests/qtest/logger/c-exp-warn
@@ -0,0 +1,4 @@
+WARNING: warning.pdf: file is damaged
+WARNING: warning.pdf (offset 1556): xref not found
+WARNING: warning.pdf: Attempting to reconstruct cross-reference table
+qpdfjob json: operation succeeded with warnings
diff --git a/libtests/qtest/logger/normal.pdf b/libtests/qtest/logger/normal.pdf
new file mode 100644
index 00000000..a7e01f91
--- /dev/null
+++ b/libtests/qtest/logger/normal.pdf
@@ -0,0 +1,79 @@
+%PDF-1.3
+1 0 obj
+<<
+  /Type /Catalog
+  /Pages 2 0 R
+>>
+endobj
+
+2 0 obj
+<<
+  /Type /Pages
+  /Kids [
+    3 0 R
+  ]
+  /Count 1
+>>
+endobj
+
+3 0 obj
+<<
+  /Type /Page
+  /Parent 2 0 R
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diff --git a/libtests/qtest/logger/warning.pdf b/libtests/qtest/logger/warning.pdf
new file mode 100644
index 00000000..e8a7042c
--- /dev/null
+++ b/libtests/qtest/logger/warning.pdf
@@ -0,0 +1,79 @@
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diff --git a/manual/release-notes.rst b/manual/release-notes.rst
index f7d673e7..f0e54db9 100644
--- a/manual/release-notes.rst
+++ b/manual/release-notes.rst
@@ -158,6 +158,8 @@ For a detailed list of changes, please see the file
         output and errors that slipped through the cracks with
         ``setOutputStreams``.
 
+      - A C API is available in :file:`include/qpdf/qpdflogger-c.h`.
+
     - New methods ``insertItemAndGet``, ``appendItemAndGet``,
       ``eraseItemAndGet``, ``replaceKeyAndGet``, and
       ``removeKeyAndGet`` return the newly added or removed object.