Do not sniff mime types

.github/workflows/test.yml

@@ -68,8 +68,6 @@ jobs:
         include:
           - target: x86_64-unknown-linux-gnu
             os: ubuntu-latest
-            # On Linux link against libmagic, since it's almost always available
-            cargo_opts: "--features magic"
           - target: x86_64-unknown-linux-musl
             os: ubuntu-latest
             cargo_opts: "--no-default-features --features static"

CHANGELOG.md

@@ -8,17 +8,17 @@ Use `cargo release` to create a new release.
 
 ## [Unreleased]
 
-### Added
-- With `--features magic` use `libmagic` to check for SVG data, instead of shelling out to `file` (see [GH-236]).
-
 ### Changed
 - Update all dependencies.
+- No longer sniff mime type from contents to identify SVG images.
+  Instead rely on the `Content-Type` header for HTTP(S) images and the file extension for local resources (see [GH-239]).
 
 ### Fixed
 - Use `less -r` instead of `less -R` in `mdless` if both `$PAGER` and `$MDCAT_PAGER` are unset (see [GH-238]).
 
 [GH-236]: https://github.com/swsnr/mdcat/pull/236
 [GH-238]: https://github.com/swsnr/mdcat/issues/238
+[GH-239]: https://github.com/swsnr/mdcat/pull/239
 
 ## [1.0.0] – 2023-01-07
 

Cargo.toml

@@ -28,14 +28,14 @@ env_proxy = "0.4.1"
 gethostname = "0.4.1"
 image = "0.24.5"
 mime = "0.3.16"
+mime_guess = "2.0.4"
 pulldown-cmark = { version = "0.9.2", default-features = false, features = ['simd'] }
 shell-words = "1.1.0"
 tracing = { version = "0.1.37", features = ["release_max_level_warn"] }
 tracing-subscriber = { version = "0.3.16", features = ["env-filter"] }
 url = "2.3.1"
 reqwest = { version = "0.11.14", default-features = false, features = ["gzip", "brotli", "blocking"]}
 once_cell = "1.17.0"
-magic = { version = "0.13.0", optional = true }
 
 [dependencies.syntect]
 version = "5.0.0"

README.md

@@ -72,15 +72,19 @@ Try `mdcat --help` or read the [mdcat(1)](./mdcat.1.adoc) manpage.
     * [Chocolatey]: `choco install mdcat`
 * You can also build `mdcat` manually with `cargo install mdcat`.
 
+[Homebrew]: https://brew.sh
+[MacPorts]: https://www.macports.org
+[Arch Linux]: https://www.archlinux.org/packages/community/x86_64/mdcat/
+[scoop]: https://github.com/lukesampson/scoop
+[chocolatey]: https://github.com/chocolatey
+
 ## Building
 
 Run `cargo build --release`.
 The resulting `mdcat` executable links against the system's SSL library, i.e. openssl on Linux.
 To build a self-contained executable use `cargo build --features=static`; the resulting executable uses a pure Rust SSL implementation.
 It still uses the system's CA roots however.
 
-Pass `--features magic` to use `libmagic` instead of the `file` program to check mimetypes.
-
 The build process also generates the following additional files in `$OUT_DIR`:
 
 * Completions for Bash, Zsh, Fish, and Powershell, for both `mdcat` and `mdless`, in `completions` sub-directory.
@@ -92,16 +96,6 @@ If you package mdcat you may want to include these files too.
 
 [AsciiDoctor]: https://asciidoctor.org/
 
-## Requirements
-
-If `mdcat` wasn't built with the `magic` feature, image type detection requires the `file` tool with support for `--brief` and `--mime-type` flags to be available in `$PATH`.
-
-[Homebrew]: https://brew.sh
-[MacPorts]: https://www.macports.org
-[Arch Linux]: https://www.archlinux.org/packages/community/x86_64/mdcat/
-[scoop]: https://github.com/lukesampson/scoop
-[chocolatey]: https://github.com/chocolatey
-
 ## Troubleshooting
 
 `mdcat` can output extensive tracing information when asked to.

mdcat.1.adoc

@@ -53,10 +53,7 @@ In particular this disables all image support which relies on proprietary escape
 In iTerm2, Kitty, Terminology and WezTerm mdcat prints inline images.
 mdcat supports most standard pixel formats by default.
 
-mdcat silently ignores images larger than 100 MiB.
-
-For some terminals mdcat needs to detect the mimetype.
-If `mdcat` was not built with `libmagic` (see output of `--version` to check) it uses the `file --brief --mime-type` for this purpose, and thus requires a compatible `file` utility in `$PATH`.
+mdcat silently ignores images larger than 100 MiB, under the assumption that images of that size cannot reasonably be rendered in a terminal.
 
 === SVG support
 
@@ -65,6 +62,9 @@ In Terminology mdcat also renders SVG images, using the built-in support of Term
 In iTerm2, Kitty and WezTerm mdcat requires `rsvg-convert` to render SVG images to pixel graphics before displaying them;
 if `rsvg-convert` is not found in `$PATH` mdcat does not render SVG images in these terminals.
 
+For local SVG files mdcat relies on the file extension to identify SVG images.
+For remote images from HTTP(S) URLs mdcat inspects the `Content-Type` header to identify SVG images.
+
 === HTTP/HTTPS support
 
 mdcat fetches images from HTTP(S) URLs for rendering if the underlying terminal supports image rendering;

src/lib.rs

@@ -22,7 +22,6 @@ use crate::terminal::capabilities::TerminalCapabilities;
 use crate::terminal::TerminalSize;
 use url::Url;
 
-mod magic;
 mod references;
 mod resources;
 mod svg;