sl4f_lib/traceutil/
facade.rs

1// Copyright 2019 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use anyhow::Error;
6use base64::engine::general_purpose::STANDARD as BASE64_STANDARD;
7use base64::engine::Engine as _;
8use serde_json::{to_value, Value};
9
10use std::collections::HashMap;
11use std::fs::File;
12use std::io::{Read, Seek, SeekFrom};
13
14/// Perform Traceutil operations.
15///
16/// Note this object is shared among all threads created by server.
17///
18/// This facade does not hold onto a Traceutil proxy as the server may be
19/// long-running while individual tests set up and tear down Traceutil.
20///
21/// WARNING: Use of this facade is discouraged as its functionality is only to download traces that
22/// were collected through other means (such as running the trace binary over ssh). Instead, see
23/// TracingFacade, which allows for control of the tracing system as well.
24#[derive(Debug)]
25pub struct TraceutilFacade {}
26
27// Chunk size of 8 MiB. Because we read a full chunk into memory and convert it
28// to base64, in cases where the system is close to OOM, a small chunk size
29// makes it more likely that we can successfully download the trace. On the other
30// hand, a very small chunk size slows down the trace download. Empirically, 8 MiB
31// seems to be a reasonable compromise.
32const MAX_CHUNK_SIZE: usize = 8 * 1024 * 1024;
33
34impl TraceutilFacade {
35    pub fn new() -> TraceutilFacade {
36        TraceutilFacade {}
37    }
38
39    /// Gets data from the specified path starting from an optional offset.
40    ///
41    /// Loading and returning the entire file is problematic for large trace files,
42    /// so will return up to |MAX_CHUNK_SIZE| bytes at once. The bytes of the file are
43    /// returned in a field called |data|. If there is more data to read, then a field
44    /// |next_offset| will be returned that indicates where it left off.
45    pub async fn get_trace_file(&self, args: Value) -> Result<Value, Error> {
46        let path = args.get("path").ok_or_else(|| format_err!("GetTraceFile failed, no path"))?;
47        let path =
48            path.as_str().ok_or_else(|| format_err!("GetTraceFile failed, path not string"))?;
49        let offset = args.get("offset").and_then(Value::as_u64).unwrap_or(0);
50
51        let mut file = File::open(path)?;
52        file.seek(SeekFrom::Start(offset))?;
53
54        let mut contents = Vec::new();
55        file.by_ref().take(MAX_CHUNK_SIZE as u64).read_to_end(&mut contents)?;
56
57        let encoded_contents = BASE64_STANDARD.encode(&contents);
58
59        let mut result: HashMap<String, Value> = HashMap::new();
60        result.insert("data".to_owned(), to_value(encoded_contents)?);
61        if contents.len() == MAX_CHUNK_SIZE {
62            let new_offset = file.seek(SeekFrom::Current(0))?;
63            result.insert("next_offset".to_owned(), to_value(new_offset)?);
64        }
65
66        Ok(to_value(result)?)
67    }
68}
sl4f_lib/traceutil/facade.rs

sl4f_lib/traceutil/
facade.rs
