Add pub struct Formatter to defmt_decoder::log.

CHANGELOG.md

@@ -7,12 +7,14 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- [#781]: `defmt-decoder`: Add `pub struct Formatter` to `defmt_decoder::log`
 - [#778]: `defmt-decoder`: Add support for nested log formatting
 - [#777]: `defmt-decoder`: Simplify StdoutLogger
 - [#775]: `defmt-decoder`: Ignore AArch64 mapping symbols
 - [#771]: `defmt-macros`: Ignore empty items in DEFMT_LOG
 - [#769]: `defmt-decoder`: Add support for color, style, width and alignment to format
 
+[#781]: https://github.com/knurling-rs/defmt/pull/781
 [#778]: https://github.com/knurling-rs/defmt/pull/778
 [#777]: https://github.com/knurling-rs/defmt/pull/777
 [#775]: https://github.com/knurling-rs/defmt/pull/775

decoder/src/lib.rs

@@ -29,13 +29,15 @@ use std::{
 };
 
 use byteorder::{ReadBytesExt, LE};
-use decoder::Decoder;
 use defmt_parser::Level;
-use elf2table::parse_impl;
 
-pub use elf2table::{Location, Locations};
-pub use frame::Frame;
-pub use stream::StreamDecoder;
+use crate::{decoder::Decoder, elf2table::parse_impl};
+
+pub use crate::{
+    elf2table::{Location, Locations},
+    frame::Frame,
+    stream::StreamDecoder,
+};
 
 /// Specifies the origin of a format string
 #[derive(PartialEq, Eq, Debug)]

decoder/src/log/mod.rs

@@ -10,12 +10,16 @@ mod format;
 mod json_logger;
 mod stdout_logger;
 
+use std::fmt;
+
 use log::{Level, LevelFilter, Log, Metadata, Record};
 use serde::{Deserialize, Serialize};
 
-use std::fmt;
-
-use self::{json_logger::JsonLogger, stdout_logger::StdoutLogger};
+use self::{
+    format::{LogMetadata, LogSegment},
+    json_logger::JsonLogger,
+    stdout_logger::{Printer, StdoutLogger},
+};
 use crate::Frame;
 
 const DEFMT_TARGET_MARKER: &str = "defmt@";
@@ -27,18 +31,7 @@ pub fn log_defmt(
     line: Option<u32>,
     module_path: Option<&str>,
 ) {
-    let timestamp = frame
-        .display_timestamp()
-        .map(|ts| ts.to_string())
-        .unwrap_or_default();
-
-    let level = frame.level().map(|level| match level {
-        crate::Level::Trace => Level::Trace,
-        crate::Level::Debug => Level::Debug,
-        crate::Level::Info => Level::Info,
-        crate::Level::Warn => Level::Warn,
-        crate::Level::Error => Level::Error,
-    });
+    let (timestamp, level) = timestamp_and_level_from_frame(frame);
 
     let target = format!(
         "{}{}",
@@ -64,7 +57,7 @@ pub fn is_defmt_frame(metadata: &Metadata) -> bool {
 }
 
 /// A `log` record representing a defmt log frame.
-pub struct DefmtRecord<'a> {
+struct DefmtRecord<'a> {
     log_record: &'a Record<'a>,
     payload: Payload,
 }
@@ -170,3 +163,79 @@ impl DefmtLoggerInfo {
         self.has_timestamp
     }
 }
+
+/// Format [`Frame`]s according to a `log_format`.
+///
+/// The `log_format` makes it possible to customize the defmt output.
+///
+/// The `log_format` is specified here: TODO
+// TODO:
+// - use two Formatter in StdoutLogger instead of the log format
+// - add fn format_to_sink
+// - specify log format
+// - clarify relationship between Formatter and Printer (https://github.com/knurling-rs/defmt/pull/781#discussion_r1343000073)
+#[derive(Debug)]
+pub struct Formatter {
+    format: Vec<LogSegment>,
+}
+
+impl Formatter {
+    pub fn new(log_format: &str) -> Self {
+        let format = format::parse(log_format)
+            .unwrap_or_else(|_| panic!("log format is invalid '{log_format}'"));
+        Self { format }
+    }
+
+    pub fn format_to_string(
+        &self,
+        frame: Frame<'_>,
+        file: Option<&str>,
+        line: Option<u32>,
+        module_path: Option<&str>,
+    ) -> String {
+        let (timestamp, level) = timestamp_and_level_from_frame(&frame);
+
+        // HACK: use match instead of let, because otherwise compilation fails
+        #[allow(clippy::match_single_binding)]
+        match format_args!("{}", frame.display_message()) {
+            args => {
+                let log_record = &Record::builder()
+                    .args(args)
+                    .module_path(module_path)
+                    .file(file)
+                    .line(line)
+                    .build();
+
+                let record = DefmtRecord {
+                    log_record,
+                    payload: Payload { level, timestamp },
+                };
+
+                match level {
+                    Some(_) => Printer::new_defmt(&record, &self.format),
+                    None => {
+                        // handle defmt::println separately
+                        const RAW_FORMAT: &[LogSegment] = &[LogSegment::new(LogMetadata::Log)];
+                        Printer::new_defmt(&record, RAW_FORMAT)
+                    }
+                }
+                .format_frame()
+            }
+        }
+    }
+}
+
+fn timestamp_and_level_from_frame(frame: &Frame<'_>) -> (String, Option<Level>) {
+    let timestamp = frame
+        .display_timestamp()
+        .map(|ts| ts.to_string())
+        .unwrap_or_default();
+    let level = frame.level().map(|level| match level {
+        crate::Level::Trace => Level::Trace,
+        crate::Level::Debug => Level::Debug,
+        crate::Level::Info => Level::Info,
+        crate::Level::Warn => Level::Warn,
+        crate::Level::Error => Level::Error,
+    });
+    (timestamp, level)
+}

decoder/src/log/stdout_logger.rs

@@ -131,50 +131,66 @@ impl StdoutLogger {
 }
 
 /// Printer for `DefmtRecord`s.
-struct Printer<'a> {
+pub(super) struct Printer<'a> {
     record: Record<'a>,
     format: &'a [LogSegment],
     min_timestamp_width: usize,
 }
 
 impl<'a> Printer<'a> {
-    pub fn new(record: Record<'a>, format: &'a [LogSegment]) -> Self {
+    fn new(record: Record<'a>, format: &'a [LogSegment]) -> Self {
         Self {
             record,
             format,
             min_timestamp_width: 0,
         }
     }
 
+    pub fn new_defmt(record: &'a DefmtRecord<'a>, format: &'a [LogSegment]) -> Self {
+        Self::new(Record::Defmt(record), format)
+    }
+
     /// Pads the defmt timestamp to take up at least the given number of characters.
     /// TODO: Remove this, shouldn't be needed now that we have width field support
-    pub fn min_timestamp_width(&mut self, min_timestamp_width: usize) -> &mut Self {
+    fn min_timestamp_width(&mut self, min_timestamp_width: usize) -> &mut Self {
         self.min_timestamp_width = min_timestamp_width;
         self
     }
 
     /// Prints the formatted log frame to `sink`.
     pub fn print_frame<W: io::Write>(&self, sink: &mut W) -> io::Result<()> {
         for segment in self.format {
-            let s = match &segment.metadata {
-                LogMetadata::String(s) => s.to_string(),
-                LogMetadata::Timestamp => self.build_timestamp(&segment.format),
-                LogMetadata::FileName => self.build_file_name(&segment.format),
-                LogMetadata::FilePath => self.build_file_path(&segment.format),
-                LogMetadata::ModulePath => self.build_module_path(&segment.format),
-                LogMetadata::LineNumber => self.build_line_number(&segment.format),
-                LogMetadata::LogLevel => self.build_log_level(&segment.format),
-                LogMetadata::Log => self.build_log(&segment.format),
-                LogMetadata::NestedLogSegments(segments) => {
-                    self.build_nested(segments, &segment.format)
-                }
-            };
-
+            let s = self.build_segment(segment);
             write!(sink, "{s}")?;
         }
         writeln!(sink)
     }
 
+    pub(super) fn format_frame(&self) -> String {
+        let mut buf = String::new();
+        for segment in self.format {
+            let s = self.build_segment(segment);
+            write!(buf, "{s}").expect("writing to String cannot fail");
+        }
+        buf
+    }
+
+    fn build_segment(&self, segment: &LogSegment) -> String {
+        match &segment.metadata {
+            LogMetadata::String(s) => s.to_string(),
+            LogMetadata::Timestamp => self.build_timestamp(&segment.format),
+            LogMetadata::FileName => self.build_file_name(&segment.format),
+            LogMetadata::FilePath => self.build_file_path(&segment.format),
+            LogMetadata::ModulePath => self.build_module_path(&segment.format),
+            LogMetadata::LineNumber => self.build_line_number(&segment.format),
+            LogMetadata::LogLevel => self.build_log_level(&segment.format),
+            LogMetadata::Log => self.build_log(&segment.format),
+            LogMetadata::NestedLogSegments(segments) => {
+                self.build_nested(segments, &segment.format)
+            }
+        }
+    }
+
     fn build_nested(&self, segments: &[LogSegment], format: &LogFormat) -> String {
         let mut result = String::new();
         for segment in segments {