Just read a chunk, encode it, write it out, and go on to the next chunk. There is no need to retain left-over symbols (either six- or eight-bit) from one chunk to the next. So if you read from the input file in chunks of 8151 (=57*143) bytes you will get (up to) 8151 eight-bit symbols, which encode as exactly 10868 six-bit symbols, which then wrap to exactly 143 MIME-formatted lines. Finally, PHP's default buffer size is 8192 bytes - enough for 143 MIME lines' worth of input. Reading 57 eight-bit symbols provides exactly enough data for a complete MIME-formatted line. 76 characters is enough for 19 quadruples of six-bit symbols thus representing 19 triples of eight-bit symbols. MIME additionally enforces a line length of 76 characters plus the CRLF. Reading the input file in chunks that are a multiple of three bytes in length results in a chunk that can be encoded independently of the rest of the input file. Other Base64 variations share the same property but they use different symbols in the last two values.Getting Started Introduction A simple tutorial Language Reference Basic syntax Types Variables Constants Expressions Operators Control Structures Functions Classes and Objects Namespaces Enumerations Errors Exceptions Fibers Generators Attributes References Explained Predefined Variables Predefined Exceptions Predefined Interfaces and Classes Predefined Attributes Context options and parameters Supported Protocols and Wrappers Security Introduction General considerations Installed as CGI binary Installed as an Apache module Session Security Filesystem Security Database Security Error Reporting User Submitted Data Hiding PHP Keeping Current Features HTTP authentication with PHP Cookies Sessions Dealing with XForms Handling file uploads Using remote files Connection handling Persistent Database Connections Command line usage Garbage Collection DTrace Dynamic Tracing Function Reference Affecting PHP's Behaviour Audio Formats Manipulation Authentication Services Command Line Specific Extensions Compression and Archive Extensions Cryptography Extensions Database Extensions Date and Time Related Extensions File System Related Extensions Human Language and Character Encoding Support Image Processing and Generation Mail Related Extensions Mathematical Extensions Non-Text MIME Output Process Control Extensions Other Basic Extensions Other Services Search Engine Extensions Server Specific Extensions Session Extensions Text Processing Variable and Type Related Extensions Web Services Windows Only Extensions XML Manipulation GUI Extensions Keyboard Shortcuts ? This help j Next menu item k Previous menu item g p Previous man page g n Next man page G Scroll to bottom g g Scroll to top g h Goto homepage g s Goto searchīase64 encoding converts triples of eight-bit symbols into quadruples of six-bit symbols. The Base64 implementation in MIME uses a-z, A-Z and 0-9 for the first 62 values. This mixture leaves the data impossible to be altered in transportation thru information systems, such as electronic mail, that were typically not 8-bit clean. The common concept is to select a set of 64 characters that is both part of a subset typical to most encodings. The specific set of characters chosen for the 64 characters needed for the base can vary among implementations. Base64 is generally used in a number of applications including electronic mail via MIME, and keeping complex information in XML. This guarantees that the data stays unchanged without modification during transfer. Types of URI charactersīase64 encoding schemes are generally used when there is a need to encode binary information that needs to be stored and transferred over media that are developed to deal with textual information. Basically, Base64 is a collection of related encoding designs which represent the binary information in ASCII format by converting it into a base64 representation. The term Base64 is coming from a certain MIME content transfer encoding.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |