Ambiguous extensions: default to first format, provide forceable fallback

This also registers the Netpbm.jl package

Author: timholy

src/FileIO.jl

@@ -86,6 +86,19 @@ function save(s::@compat(Union{AbstractString,IO}), data...; options...)
     rethrow(last_exception)
 end
 
+# Forced format
+function save{sym}(::Type{DataFormat{sym}}, f::AbstractString, data...; options...)
+    libraries = sym2saver[sym]
+    check_saver(libraries[1])
+    save(File(DataFormat{sym}, f), data...; options...)
+end
+
+function save{sym}(::Type{DataFormat{sym}}, s::IO, data...; options...)
+    libraries = sym2saver[sym]
+    check_saver(libraries[1])
+    save(Stream(DataFormat{sym}, s), data...; options...)
+end
+
 function Base.writemime(io::IO, mime::MIME, x)
     handlers = applicable_mime(mime)
     last_exception = ErrorException("No package available to writemime $mime")

src/query.jl

@@ -352,7 +352,7 @@ function query(filename::AbstractString)
         if lensym(sym) == 1 && (no_magic || !isfile(filename)) # we only found one candidate and there is no magic bytes, or no file, trust the extension
             return File{DataFormat{sym}}(filename)
         elseif !isfile(filename) && lensym(sym) > 1
-            error("no file for check of magic bytes and multiple extensions possible: $sym")
+            return File{DataFormat{sym[1]}}(filename)
         end
         if no_magic && !hasfunction(sym)
             error("Some formats with extension ", ext, " have no magic bytes; use `File{format\"FMT\"}(filename)` to resolve the ambiguity.")

src/registry.jl

@@ -2,12 +2,12 @@
 add_format(format"JLD", "Julia data file (HDF5)", ".jld", [:JLD])
 
 # Image formats
-add_format(format"PBMText",   b"P1", ".pbm")
-add_format(format"PGMText",   b"P2", ".pgm")
-add_format(format"PPMText",   b"P3", ".ppm")
-add_format(format"PBMBinary", b"P4", ".pbm")
-add_format(format"PGMBinary", b"P5", ".pgm")
-add_format(format"PPMBinary", b"P6", ".ppm")
+add_format(format"PBMBinary", b"P4", ".pbm", [:ImageMagick])
+add_format(format"PGMBinary", b"P5", ".pgm", [:Netpbm])
+add_format(format"PPMBinary", b"P6", ".ppm", [:Netpbm])
+add_format(format"PBMText",   b"P1", ".pbm", [:ImageMagick, LOAD])
+add_format(format"PGMText",   b"P2", ".pgm", [:ImageMagick, LOAD])
+add_format(format"PPMText",   b"P3", ".ppm", [:ImageMagick, LOAD])
 
 add_format(format"NRRD", "NRRD", [".nrrd", ".nhdr"], [:NRRD])
 

test/REQUIRE

@@ -1 +1,4 @@
 FactCheck
+Images
+Netpbm
+ImageMagick

test/loadsave.jl

@@ -115,3 +115,23 @@ context("Save") do
 end
 
 del_format(format"DUMMY")
+
+# PPM/PBM can be either binary or text. Test that the defaults work,
+# and that we can force a choice.
+using Images
+context("Ambiguous extension") do
+    A = rand(UInt8, 3, 2)
+    fn = string(tempname(), ".pgm")
+    # Test the forced version first: we wouldn't want some method in Netpbm
+    # coming to the rescue here, we want to rely on FileIO's logic.
+    # `save(fn, A)` will load Netpbm, which could conceivably mask a failure
+    # in the next line.
+    save(format"PGMBinary", fn, A)
+    B = load(fn)
+    @fact raw(convert(Array, B)) --> A
+    save(fn, A)
+    B = load(fn)
+    @fact raw(convert(Array, B)) --> A
+
+    rm(fn)
+end