22. Physical computer storage that comprises a computer readable storage medium, said physical computer storage having stored thereon instructions that, when executed, direct a computing system to: determine that a URL (Uniform Resource Locator) received from a user computing device is invalid, the URL including a name of a domain and a character string, the character string including a first product identifier; at least partly in response to the invalid URL request, through a conversion process, converting the invalid URL into a repaired URL, the repaired URL different from the invalid URL, the conversion process comprising: identifying a non-URL escape sequence in the character string, the escape sequence corresponding to a special character; replacing the non-URL escape sequence in the character string with the corresponding special character; and decoding the URL a second time by replacing a URL escape sequence in the character string with a corresponding special character, wherein the URL was previously decoded a first time; and in response to determining whether the repaired URL resolves to valid content, (1) provide the valid content associated with the repaired URL to the user computing device when the repaired URL is valid or (2) identify, using the first product identifier extracted from the invalid URL, a substitute URL and provide content associated with the substitute URL when the repaired URL is invalid.
24. The physical computer storage of claim 22 , further comprising instructions that, when executed, direct a computing system to sanitize the URL before the conversion process by excluding some characters from the conversion process.