Scala-IO Core: Seekable

At the same level of abstraction as Input and Output is the fine trait called Seekable.  As the name implies it provides random access style methods for interacting with a resource.  The example that comes immediately to mind is a random access file.

The design of Seekable largely mimics the scala.collection.Seq patch and insert methods.  Not much more to say beyond getting into some examples:

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import scalax.io._ import java.io.File   // For this example lets explicitly specify a codec implicit val codec = scalax.io.Codec.UTF8   val file: Seekable =  Resource.fromFile(new File("scala-io.out"))   // delete all data from the file // or more specifically only keep the data from the beginning of the // file up to (but not including) the first byte file truncate 0   val seedData = "Entering some seed data into the file" file write seedData   // verify seed data was correctly written (in REPL) file.string     // write "first" after character 9 // if the file is < 9 characters an underflow exception is thrown // if the patch extends past the end of the file then the file is extended // Note: The offset is always dependent on type of data being written // for example if the data written is a string it will be 9 characters // if the data is bytes it will be 9 bytes file patch (9, "first",OverwriteAll)   // dumping to REPL will show: Entering firstseed data into the file file.string   // patch at position 0 and replace 100 bytes with new data file.patch(0,seedData, OverwriteSome(100))   // dumping to REPL will show the unchanged seedData once again file.string   // Overwrite only 4 bytes starting at bytes 9. // the extra bytes will be inserted // In other words the "some" word of seed data will // be replaced with second // Warning: This is an overwrite and an insert // inserts are expensive since it requires copying the data from // the index to end of file.  If small enough it is done in // memory but a temporary file is required for big files. file.patch(9,"second".getBytes(), OverwriteSome(4))   // dumping to REPL will show: Entering second seed data into the file file.string   // reset file file.patch(0,seedData, OverwriteSome(100))   // Replace 9 bytes with the 5 bytes that are provided // In other words: replace "some seed" with "third" file.patch(9,"third".getBytes(), OverwriteSome(9))   // dumping to REPL will show: Entering third data into the file file.string   // reset file file.patch(0,seedData, OverwriteSome(100))   // Insert a string at start of file file.insert(0, "newInsertedData ")   // dumping to REPL will show: newInsertedData Entering some seed data into the file file.string   // reset file file.patch(0,seedData, OverwriteSome(100))   //add !! to end of file file.append("!!")   // dumping to REPL will show: Entering some seed data into the file!! file.string

IMPORTANT: Each time truncate() or patch or insert is called a new connection to the file is opened and closed. The Processor API is to be used to perform multiple operations within one connection.

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import scalax.io._ import java.io.File   val file: Seekable =  Resource.fromFile(new File("scala-io.out"))   for {   p <- file.seekableProcessor   seekable = p.asSeekable } {   seekable truncate 0   seekable write "hi"   seekable append " world"     // one can do patch, insert etc...   // or move the cursor to the correct position and write   // this is essentially a patch(0, "Hi", OverwriteAll)   seekable.position = 0   seekable write "Hi"     seekable patch (3, "W", OverwriteAll)     // dumping to REPL will show: Hi World   println (seekable.string) }